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 $59.86   5.419%   $63.1038   $63.10   $63.10   $63.10  
  Purchase #2 $18.47   4.191%   $19.2441   $19.24   $19.25   $19.20  
  Purchase #3 $234.71   9.610%   $257.2656   $257.27   $257.25   $257.30  
  Purchase #4 $45.54   7.764%   $49.0757   $49.08   $49.10   $49.10  
  Purchase #5 $179.77   5.250%   $189.2079   $189.21   $189.20   $189.20  
  Purchase #6 $170.28   12.198%   $191.0508   $191.05   $191.05   $191.10  
  Purchase #7 $23.42   9.256%   $25.5878   $25.59   $25.60   $25.60  
  7 purchase totals = $732.05       $794.5357   $794.54   $794.55   $794.60