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 $5.76   13.213%   $6.5211   $6.52   $6.50   $6.50  
  Purchase #2 $134.33   13.654%   $152.6714   $152.67   $152.65   $152.70  
  Purchase #3 $203.32   10.579%   $224.8292   $224.83   $224.85   $224.80  
  Purchase #4 $37.92   6.454%   $40.3674   $40.37   $40.35   $40.40  
  Purchase #5 $200.97   9.818%   $220.7012   $220.70   $220.70   $220.70  
  Purchase #6 $85.61   11.630%   $95.5664   $95.57   $95.55   $95.60  
  Purchase #7 $202.71   5.484%   $213.8266   $213.83   $213.85   $213.80  
  7 purchase totals = $870.62       $954.4833   $954.49   $954.45   $954.50