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 $246.76   10.718%   $273.2077   $273.21   $273.20   $273.20  
  Purchase #2 $182.36   7.144%   $195.3878   $195.39   $195.40   $195.40  
  Purchase #3 $51.36   5.815%   $54.3466   $54.35   $54.35   $54.30  
  Purchase #4 $244.36   5.541%   $257.9   $257.90   $257.90   $257.90  
  Purchase #5 $131.52   5.156%   $138.3012   $138.30   $138.30   $138.30  
  Purchase #6 $206.94   6.538%   $220.4697   $220.47   $220.45   $220.50  
  Purchase #7 $68.49   4.287%   $71.4262   $71.43   $71.45   $71.40  
  7 purchase totals = $1,131.79       $1,211.0392   $1,211.05   $1,211.05   $1,211.00