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 $57.68   9.808%   $63.3373   $63.34   $63.35   $63.30  
  Purchase #2 $204.75   7.207%   $219.5063   $219.51   $219.50   $219.50  
  Purchase #3 $113.52   3.605%   $117.6124   $117.61   $117.60   $117.60  
  Purchase #4 $109.96   10.183%   $121.1572   $121.16   $121.15   $121.20  
  Purchase #5 $209.85   9.261%   $229.2842   $229.28   $229.30   $229.30  
  Purchase #6 $52.91   13.764%   $60.1925   $60.19   $60.20   $60.20  
  Purchase #7 $125.35   13.172%   $141.8611   $141.86   $141.85   $141.90  
  7 purchase totals = $874.02       $952.9510   $952.95   $952.95   $953.00