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 $193.77   5.144%   $203.7375   $203.74   $203.75   $203.70  
  Purchase #2 $55.85   11.597%   $62.3269   $62.33   $62.35   $62.30  
  Purchase #3 $28.56   4.522%   $29.8515   $29.85   $29.85   $29.90  
  Purchase #4 $62.99   6.198%   $66.8941   $66.89   $66.90   $66.90  
  Purchase #5 $10.39   4.378%   $10.8449   $10.84   $10.85   $10.80  
  Purchase #6 $224.31   3.476%   $232.107   $232.11   $232.10   $232.10  
  Purchase #7 $131.95   6.778%   $140.8936   $140.89   $140.90   $140.90  
  7 purchase totals = $707.82       $746.6555   $746.65   $746.70   $746.60