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 $236.43   12.649%   $266.336   $266.34   $266.35   $266.30  
  Purchase #2 $33.36   8.427%   $36.1712   $36.17   $36.15   $36.20  
  Purchase #3 $235.42   3.794%   $244.3518   $244.35   $244.35   $244.40  
  Purchase #4 $66.86   13.786%   $76.0773   $76.08   $76.10   $76.10  
  Purchase #5 $202.52   10.191%   $223.1588   $223.16   $223.15   $223.20  
  Purchase #6 $130.71   5.340%   $137.6899   $137.69   $137.70   $137.70  
  Purchase #7 $58.37   4.764%   $61.1507   $61.15   $61.15   $61.20  
  7 purchase totals = $963.67       $1,044.9357   $1,044.94   $1,044.95   $1,045.10