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 $201.27   12.599%   $226.628   $226.63   $226.65   $226.60  
  Purchase #2 $10.85   3.369%   $11.2155   $11.22   $11.20   $11.20  
  Purchase #3 $158.37   3.686%   $164.2075   $164.21   $164.20   $164.20  
  Purchase #4 $41.90   3.266%   $43.2685   $43.27   $43.25   $43.30  
  Purchase #5 $159.78   8.352%   $173.1248   $173.12   $173.10   $173.10  
  Purchase #6 $173.67   4.505%   $181.4938   $181.49   $181.50   $181.50  
  Purchase #7 $58.35   5.515%   $61.568   $61.57   $61.55   $61.60  
  7 purchase totals = $804.19       $861.5061   $861.51   $861.45   $861.50