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 $47.38   9.683%   $51.9678   $51.97   $51.95   $52.00  
  Purchase #2 $187.55   7.718%   $202.0251   $202.03   $202.05   $202.00  
  Purchase #3 $108.66   8.867%   $118.2949   $118.29   $118.30   $118.30  
  Purchase #4 $151.87   13.840%   $172.8888   $172.89   $172.90   $172.90  
  Purchase #5 $224.84   6.538%   $239.54   $239.54   $239.55   $239.50  
  Purchase #6 $217.99   12.623%   $245.5069   $245.51   $245.50   $245.50  
  Purchase #7 $218.74   6.578%   $233.1287   $233.13   $233.15   $233.10  
  7 purchase totals = $1,157.03       $1,263.3522   $1,263.36   $1,263.40   $1,263.30