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 $63.57   3.790%   $65.9793   $65.98   $66.00   $66.00  
  Purchase #2 $202.41   4.293%   $211.0995   $211.10   $211.10   $211.10  
  Purchase #3 $92.71   6.629%   $98.8557   $98.86   $98.85   $98.90  
  Purchase #4 $14.29   4.445%   $14.9252   $14.93   $14.95   $14.90  
  Purchase #5 $48.56   11.149%   $53.974   $53.97   $53.95   $54.00  
  Purchase #6 $93.81   4.556%   $98.084   $98.08   $98.10   $98.10  
  Purchase #7 $104.64   10.216%   $115.33   $115.33   $115.35   $115.30  
  7 purchase totals = $619.99       $658.2477   $658.25   $658.30   $658.30