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 $77.68   9.281%   $84.8895   $84.89   $84.90   $84.90  
  Purchase #2 $39.79   10.831%   $44.0997   $44.10   $44.10   $44.10  
  Purchase #3 $23.92   5.207%   $25.1655   $25.17   $25.15   $25.20  
  Purchase #4 $59.43   6.787%   $63.4635   $63.46   $63.45   $63.50  
  Purchase #5 $139.96   5.573%   $147.76   $147.76   $147.75   $147.80  
  Purchase #6 $245.53   3.349%   $253.7528   $253.75   $253.75   $253.80  
  Purchase #7 $109.63   11.776%   $122.54   $122.54   $122.55   $122.50  
  7 purchase totals = $695.94       $741.6710   $741.67   $741.65   $741.80