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 $64.70   5.630%   $68.3426   $68.34   $68.35   $68.30  
  Purchase #2 $189.51   7.272%   $203.2912   $203.29   $203.30   $203.30  
  Purchase #3 $122.83   9.706%   $134.7519   $134.75   $134.75   $134.80  
  Purchase #4 $6.34   11.567%   $7.0733   $7.07   $7.05   $7.10  
  Purchase #5 $52.57   5.410%   $55.414   $55.41   $55.40   $55.40  
  Purchase #6 $95.37   8.315%   $103.3   $103.30   $103.30   $103.30  
  Purchase #7 $194.45   9.538%   $212.9966   $213.00   $213.00   $213.00  
  7 purchase totals = $725.77       $785.1696   $785.16   $785.15   $785.20