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 $244.84   12.621%   $275.7413   $275.74   $275.75   $275.70  
  Purchase #2 $39.44   4.505%   $41.2168   $41.22   $41.20   $41.20  
  Purchase #3 $236.57   7.564%   $254.4642   $254.46   $254.45   $254.50  
  Purchase #4 $117.58   6.294%   $124.9805   $124.98   $125.00   $125.00  
  Purchase #5 $236.33   8.864%   $257.2783   $257.28   $257.30   $257.30  
  Purchase #6 $209.52   3.564%   $216.9873   $216.99   $217.00   $217.00  
  Purchase #7 $48.81   13.462%   $55.3808   $55.38   $55.40   $55.40  
  7 purchase totals = $1,133.09       $1,226.0492   $1,226.05   $1,226.10   $1,226.10