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 $58.43   11.774%   $65.3095   $65.31   $65.30   $65.30  
  Purchase #2 $218.33   3.138%   $225.1812   $225.18   $225.20   $225.20  
  Purchase #3 $180.36   11.588%   $201.2601   $201.26   $201.25   $201.30  
  Purchase #4 $152.30   7.303%   $163.4225   $163.42   $163.40   $163.40  
  Purchase #5 $50.37   9.261%   $55.0348   $55.03   $55.05   $55.00  
  Purchase #6 $170.94   10.617%   $189.0887   $189.09   $189.10   $189.10  
  Purchase #7 $68.46   8.864%   $74.5283   $74.53   $74.55   $74.50  
  7 purchase totals = $899.19       $973.8251   $973.82   $973.85   $973.80