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 $47.66   13.223%   $53.9621   $53.96   $53.95   $54.00  
  Purchase #2 $145.82   7.764%   $157.1415   $157.14   $157.15   $157.10  
  Purchase #3 $198.87   5.334%   $209.4777   $209.48   $209.50   $209.50  
  Purchase #4 $17.62   12.582%   $19.8369   $19.84   $19.85   $19.80  
  Purchase #5 $14.82   3.760%   $15.3772   $15.38   $15.40   $15.40  
  Purchase #6 $204.52   9.595%   $224.1437   $224.14   $224.15   $224.10  
  Purchase #7 $60.51   11.249%   $67.3168   $67.32   $67.30   $67.30  
  7 purchase totals = $689.82       $747.2559   $747.26   $747.30   $747.20