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 $189.27   10.568%   $209.2721   $209.27   $209.25   $209.30  
  Purchase #2 $53.71   4.278%   $56.0077   $56.01   $56.00   $56.00  
  Purchase #3 $137.27   4.435%   $143.3579   $143.36   $143.35   $143.40  
  Purchase #4 $85.70   6.166%   $90.9843   $90.98   $91.00   $91.00  
  Purchase #5 $68.46   11.767%   $76.5157   $76.52   $76.50   $76.50  
  Purchase #6 $135.96   5.332%   $143.2094   $143.21   $143.20   $143.20  
  Purchase #7 $123.81   7.621%   $133.2456   $133.25   $133.25   $133.20  
  7 purchase totals = $794.18       $852.5927   $852.60   $852.55   $852.60