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 $128.65   5.616%   $135.875   $135.88   $135.90   $135.90  
  Purchase #2 $187.28   10.349%   $206.6616   $206.66   $206.65   $206.70  
  Purchase #3 $230.73   7.748%   $248.607   $248.61   $248.60   $248.60  
  Purchase #4 $93.46   13.437%   $106.0182   $106.02   $106.00   $106.00  
  Purchase #5 $121.63   6.306%   $129.3   $129.30   $129.30   $129.30  
  Purchase #6 $126.99   11.279%   $141.3132   $141.31   $141.30   $141.30  
  Purchase #7 $75.76   11.613%   $84.558   $84.56   $84.55   $84.60  
  7 purchase totals = $964.50       $1,052.3330   $1,052.34   $1,052.30   $1,052.40