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 $88.71   3.356%   $91.6871   $91.69   $91.70   $91.70  
  Purchase #2 $176.31   4.811%   $184.7923   $184.79   $184.80   $184.80  
  Purchase #3 $110.27   3.773%   $114.4305   $114.43   $114.45   $114.40  
  Purchase #4 $76.65   5.343%   $80.7454   $80.75   $80.75   $80.70  
  Purchase #5 $59.47   12.703%   $67.0245   $67.02   $67.00   $67.00  
  Purchase #6 $155.59   3.372%   $160.8365   $160.84   $160.85   $160.80  
  Purchase #7 $61.84   4.170%   $64.4187   $64.42   $64.40   $64.40  
  7 purchase totals = $728.84       $763.9350   $763.94   $763.95   $763.80