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 $116.99   13.623%   $132.9275   $132.93   $132.95   $132.90  
  Purchase #2 $60.51   6.420%   $64.3947   $64.39   $64.40   $64.40  
  Purchase #3 $54.68   3.564%   $56.6288   $56.63   $56.65   $56.60  
  Purchase #4 $201.38   12.333%   $226.2162   $226.22   $226.20   $226.20  
  Purchase #5 $247.83   5.501%   $261.4631   $261.46   $261.45   $261.50  
  Purchase #6 $36.93   5.198%   $38.8496   $38.85   $38.85   $38.80  
  Purchase #7 $62.92   3.282%   $64.985   $64.99   $65.00   $65.00  
  7 purchase totals = $781.24       $845.4649   $845.47   $845.50   $845.40