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 $52.26   8.562%   $56.7345   $56.73   $56.75   $56.70  
  Purchase #2 $246.46   11.589%   $275.0222   $275.02   $275.00   $275.00  
  Purchase #3 $183.53   8.621%   $199.3521   $199.35   $199.35   $199.40  
  Purchase #4 $100.38   9.252%   $109.6672   $109.67   $109.65   $109.70  
  Purchase #5 $42.48   8.358%   $46.0305   $46.03   $46.05   $46.00  
  Purchase #6 $148.73   8.149%   $160.85   $160.85   $160.85   $160.90  
  Purchase #7 $43.31   3.841%   $44.9735   $44.97   $44.95   $45.00  
  7 purchase totals = $817.15       $892.6300   $892.62   $892.60   $892.70