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 $204.53   12.552%   $230.2026   $230.20   $230.20   $230.20  
  Purchase #2 $212.30   5.802%   $224.6176   $224.62   $224.60   $224.60  
  Purchase #3 $92.42   5.360%   $97.3737   $97.37   $97.35   $97.40  
  Purchase #4 $76.26   11.820%   $85.2739   $85.27   $85.25   $85.30  
  Purchase #5 $122.38   11.558%   $136.5247   $136.52   $136.50   $136.50  
  Purchase #6 $207.70   9.757%   $227.9653   $227.97   $227.95   $228.00  
  Purchase #7 $225.65   12.760%   $254.4429   $254.44   $254.45   $254.40  
  7 purchase totals = $1,141.24       $1,256.4007   $1,256.39   $1,256.30   $1,256.40