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 $209.52   6.189%   $222.4872   $222.49   $222.50   $222.50  
  Purchase #2 $232.96   6.290%   $247.6132   $247.61   $247.60   $247.60  
  Purchase #3 $167.47   9.380%   $183.1787   $183.18   $183.20   $183.20  
  Purchase #4 $80.84   12.694%   $91.1018   $91.10   $91.10   $91.10  
  Purchase #5 $27.77   6.562%   $29.5923   $29.59   $29.60   $29.60  
  Purchase #6 $96.88   11.417%   $107.9408   $107.94   $107.95   $107.90  
  Purchase #7 $68.80   7.402%   $73.8926   $73.89   $73.90   $73.90  
  7 purchase totals = $884.24       $955.8066   $955.80   $955.85   $955.80