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 $216.61   7.478%   $232.8081   $232.81   $232.80   $232.80  
  Purchase #2 $25.33   6.202%   $26.901   $26.90   $26.90   $26.90  
  Purchase #3 $78.41   9.733%   $86.0416   $86.04   $86.05   $86.00  
  Purchase #4 $9.51   7.185%   $10.1933   $10.19   $10.20   $10.20  
  Purchase #5 $174.72   10.461%   $192.9975   $193.00   $193.00   $193.00  
  Purchase #6 $53.45   10.602%   $59.1168   $59.12   $59.10   $59.10  
  Purchase #7 $157.77   7.407%   $169.456   $169.46   $169.45   $169.50  
  7 purchase totals = $715.80       $777.5143   $777.52   $777.50   $777.50