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 $230.92   9.420%   $252.6727   $252.67   $252.65   $252.70  
  Purchase #2 $148.75   3.801%   $154.404   $154.40   $154.40   $154.40  
  Purchase #3 $217.99   13.297%   $246.9761   $246.98   $247.00   $247.00  
  Purchase #4 $56.39   11.197%   $62.704   $62.70   $62.70   $62.70  
  Purchase #5 $20.86   5.269%   $21.9591   $21.96   $21.95   $22.00  
  Purchase #6 $36.80   11.346%   $40.9753   $40.98   $41.00   $41.00  
  Purchase #7 $68.57   5.334%   $72.2275   $72.23   $72.25   $72.20  
  7 purchase totals = $780.28       $851.9187   $851.92   $851.95   $852.00