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 $54.79   12.513%   $61.6459   $61.65   $61.65   $61.60  
  Purchase #2 $133.80   8.635%   $145.3536   $145.35   $145.35   $145.40  
  Purchase #3 $56.37   11.332%   $62.7578   $62.76   $62.75   $62.80  
  Purchase #4 $15.68   11.382%   $17.4647   $17.46   $17.45   $17.50  
  Purchase #5 $214.52   7.201%   $229.9676   $229.97   $229.95   $230.00  
  Purchase #6 $54.90   4.765%   $57.516   $57.52   $57.50   $57.50  
  Purchase #7 $136.99   3.198%   $141.3709   $141.37   $141.35   $141.40  
  7 purchase totals = $667.05       $716.0765   $716.08   $716.00   $716.20