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 $55.52   9.752%   $60.9343   $60.93   $60.95   $60.90  
  Purchase #2 $43.50   6.464%   $46.3118   $46.31   $46.30   $46.30  
  Purchase #3 $78.77   12.141%   $88.3335   $88.33   $88.35   $88.30  
  Purchase #4 $233.51   3.609%   $241.9374   $241.94   $241.95   $241.90  
  Purchase #5 $222.25   5.719%   $234.9605   $234.96   $234.95   $235.00  
  Purchase #6 $52.76   6.185%   $56.0232   $56.02   $56.00   $56.00  
  Purchase #7 $121.87   7.698%   $131.2516   $131.25   $131.25   $131.30  
  7 purchase totals = $808.18       $859.7523   $859.74   $859.75   $859.70