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 $132.60   13.131%   $150.0117   $150.01   $150.00   $150.00  
  Purchase #2 $187.27   7.329%   $200.995   $201.00   $201.00   $201.00  
  Purchase #3 $17.88   10.806%   $19.8121   $19.81   $19.80   $19.80  
  Purchase #4 $219.82   7.761%   $236.8802   $236.88   $236.90   $236.90  
  Purchase #5 $174.41   12.579%   $196.349   $196.35   $196.35   $196.30  
  Purchase #6 $224.78   6.142%   $238.586   $238.59   $238.60   $238.60  
  Purchase #7 $209.43   10.104%   $230.5908   $230.59   $230.60   $230.60  
  7 purchase totals = $1,166.19       $1,273.2248   $1,273.23   $1,273.25   $1,273.20