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 $183.47   11.504%   $204.5764   $204.58   $204.60   $204.60  
  Purchase #2 $249.48   10.385%   $275.3885   $275.39   $275.40   $275.40  
  Purchase #3 $241.29   11.753%   $269.6488   $269.65   $269.65   $269.60  
  Purchase #4 $47.99   13.862%   $54.6424   $54.64   $54.65   $54.60  
  Purchase #5 $30.89   8.167%   $33.4128   $33.41   $33.40   $33.40  
  Purchase #6 $241.98   10.649%   $267.7485   $267.75   $267.75   $267.70  
  Purchase #7 $25.93   4.443%   $27.0821   $27.08   $27.10   $27.10  
  7 purchase totals = $1,021.03       $1,132.4995   $1,132.50   $1,132.55   $1,132.40