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 $75.65   10.192%   $83.3602   $83.36   $83.35   $83.40  
  Purchase #2 $247.60   5.509%   $261.2403   $261.24   $261.25   $261.20  
  Purchase #3 $116.34   3.570%   $120.4933   $120.49   $120.50   $120.50  
  Purchase #4 $50.35   10.178%   $55.4746   $55.47   $55.45   $55.50  
  Purchase #5 $181.29   13.761%   $206.2373   $206.24   $206.25   $206.20  
  Purchase #6 $144.57   4.426%   $150.9687   $150.97   $150.95   $151.00  
  Purchase #7 $142.46   9.179%   $155.5364   $155.54   $155.55   $155.50  
  7 purchase totals = $958.26       $1,033.3108   $1,033.31   $1,033.30   $1,033.30