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 $32.95   5.688%   $34.8242   $34.82   $34.80   $34.80  
  Purchase #2 $234.91   12.464%   $264.1892   $264.19   $264.20   $264.20  
  Purchase #3 $66.78   10.158%   $73.5635   $73.56   $73.55   $73.60  
  Purchase #4 $63.88   9.618%   $70.024   $70.02   $70.00   $70.00  
  Purchase #5 $12.91   12.828%   $14.5661   $14.57   $14.55   $14.60  
  Purchase #6 $249.87   7.573%   $268.7927   $268.79   $268.80   $268.80  
  Purchase #7 $24.68   5.207%   $25.9651   $25.97   $25.95   $26.00  
  7 purchase totals = $685.98       $751.9248   $751.92   $751.85   $752.00