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 $86.67   10.527%   $95.7938   $95.79   $95.80   $95.80  
  Purchase #2 $246.52   10.719%   $272.9445   $272.94   $272.95   $272.90  
  Purchase #3 $103.27   8.676%   $112.2297   $112.23   $112.25   $112.20  
  Purchase #4 $7.73   13.324%   $8.7599   $8.76   $8.75   $8.80  
  Purchase #5 $81.49   10.184%   $89.7889   $89.79   $89.80   $89.80  
  Purchase #6 $22.75   12.306%   $25.5496   $25.55   $25.55   $25.50  
  Purchase #7 $43.78   5.260%   $46.0828   $46.08   $46.10   $46.10  
  7 purchase totals = $592.21       $651.1492   $651.14   $651.20   $651.10