Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.67   12.531%   $271.9537   $271.95   $271.95   $272.00  
  Purchase #2 $114.73   3.409%   $118.6411   $118.64   $118.65   $118.60  
  Purchase #3 $119.77   10.470%   $132.3099   $132.31   $132.30   $132.30  
  Purchase #4 $151.57   13.840%   $172.5473   $172.55   $172.55   $172.50  
  Purchase #5 $202.82   4.818%   $212.5919   $212.59   $212.60   $212.60  
  Purchase #6 $113.34   4.176%   $118.0731   $118.07   $118.05   $118.10  
  Purchase #7 $225.83   4.197%   $235.3081   $235.31   $235.30   $235.30  
  7 purchase totals = $1,169.73       $1,261.4251   $1,261.42   $1,261.40   $1,261.40