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 $91.78   4.352%   $95.7743   $95.77   $95.75   $95.80  
  Purchase #2 $146.53   13.752%   $166.6808   $166.68   $166.70   $166.70  
  Purchase #3 $16.35   3.778%   $16.9677   $16.97   $16.95   $17.00  
  Purchase #4 $11.85   12.238%   $13.3002   $13.30   $13.30   $13.30  
  Purchase #5 $89.28   5.223%   $93.9431   $93.94   $93.95   $93.90  
  Purchase #6 $235.72   6.241%   $250.4313   $250.43   $250.45   $250.40  
  Purchase #7 $53.66   11.830%   $60.008   $60.01   $60.00   $60.00  
  7 purchase totals = $645.17       $697.1054   $697.10   $697.10   $697.10