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 $226.75   7.602%   $243.9875   $243.99   $244.00   $244.00  
  Purchase #2 $158.25   4.440%   $165.2763   $165.28   $165.30   $165.30  
  Purchase #3 $35.73   5.614%   $37.7359   $37.74   $37.75   $37.70  
  Purchase #4 $11.84   12.710%   $13.3449   $13.34   $13.35   $13.30  
  Purchase #5 $72.37   6.455%   $77.0415   $77.04   $77.05   $77.00  
  Purchase #6 $205.98   10.739%   $228.1002   $228.10   $228.10   $228.10  
  Purchase #7 $24.60   9.437%   $26.9215   $26.92   $26.90   $26.90  
  7 purchase totals = $735.52       $792.4078   $792.41   $792.45   $792.30