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 $43.52   8.411%   $47.1805   $47.18   $47.20   $47.20  
  Purchase #2 $127.63   12.767%   $143.9245   $143.92   $143.90   $143.90  
  Purchase #3 $68.98   9.702%   $75.6724   $75.67   $75.65   $75.70  
  Purchase #4 $43.77   6.232%   $46.4977   $46.50   $46.50   $46.50  
  Purchase #5 $167.43   4.872%   $175.5872   $175.59   $175.60   $175.60  
  Purchase #6 $235.64   10.352%   $260.0335   $260.03   $260.05   $260.00  
  Purchase #7 $242.38   12.361%   $272.3406   $272.34   $272.35   $272.30  
  7 purchase totals = $929.35       $1,021.2364   $1,021.23   $1,021.25   $1,021.20