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 $197.39   13.479%   $223.9962   $224.00   $224.00   $224.00  
  Purchase #2 $138.53   11.625%   $154.6341   $154.63   $154.65   $154.60  
  Purchase #3 $24.86   8.244%   $26.9095   $26.91   $26.90   $26.90  
  Purchase #4 $168.48   12.167%   $188.979   $188.98   $189.00   $189.00  
  Purchase #5 $133.43   13.396%   $151.3043   $151.30   $151.30   $151.30  
  Purchase #6 $55.93   8.409%   $60.6332   $60.63   $60.65   $60.60  
  Purchase #7 $210.82   11.396%   $234.845   $234.85   $234.85   $234.80  
  7 purchase totals = $929.44       $1,041.3013   $1,041.30   $1,041.35   $1,041.20