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 $167.64   9.869%   $184.1844   $184.18   $184.20   $184.20  
  Purchase #2 $147.41   7.861%   $158.9979   $159.00   $159.00   $159.00  
  Purchase #3 $113.27   5.424%   $119.4138   $119.41   $119.40   $119.40  
  Purchase #4 $34.40   4.412%   $35.9177   $35.92   $35.90   $35.90  
  Purchase #5 $234.85   4.563%   $245.5662   $245.57   $245.55   $245.60  
  Purchase #6 $8.91   3.261%   $9.2006   $9.20   $9.20   $9.20  
  Purchase #7 $129.36   5.701%   $136.7348   $136.73   $136.75   $136.70  
  7 purchase totals = $835.84       $890.0154   $890.01   $890.00   $890.00