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 $242.47   13.278%   $274.6652   $274.67   $274.65   $274.70  
  Purchase #2 $173.48   12.689%   $195.4929   $195.49   $195.50   $195.50  
  Purchase #3 $41.86   11.793%   $46.7965   $46.80   $46.80   $46.80  
  Purchase #4 $27.51   4.786%   $28.8266   $28.83   $28.85   $28.80  
  Purchase #5 $126.52   12.263%   $142.0351   $142.04   $142.05   $142.00  
  Purchase #6 $122.64   6.739%   $130.9047   $130.90   $130.90   $130.90  
  Purchase #7 $185.50   11.400%   $206.647   $206.65   $206.65   $206.60  
  7 purchase totals = $919.98       $1,025.3680   $1,025.38   $1,025.40   $1,025.30