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 $60.65   4.228%   $63.2143   $63.21   $63.20   $63.20  
  Purchase #2 $113.91   8.804%   $123.9386   $123.94   $123.95   $123.90  
  Purchase #3 $94.76   4.515%   $99.0384   $99.04   $99.05   $99.00  
  Purchase #4 $69.50   8.257%   $75.2386   $75.24   $75.25   $75.20  
  Purchase #5 $225.30   9.471%   $246.6382   $246.64   $246.65   $246.60  
  Purchase #6 $93.39   11.682%   $104.2998   $104.30   $104.30   $104.30  
  Purchase #7 $63.63   5.580%   $67.1806   $67.18   $67.20   $67.20  
  7 purchase totals = $721.14       $779.5485   $779.55   $779.60   $779.40