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 $34.82   6.824%   $37.1961   $37.20   $37.20   $37.20  
  Purchase #2 $165.33   3.827%   $171.6572   $171.66   $171.65   $171.70  
  Purchase #3 $40.90   12.209%   $45.8935   $45.89   $45.90   $45.90  
  Purchase #4 $88.71   3.656%   $91.9532   $91.95   $91.95   $92.00  
  Purchase #5 $187.29   7.559%   $201.4473   $201.45   $201.45   $201.40  
  Purchase #6 $46.85   5.833%   $49.5828   $49.58   $49.60   $49.60  
  Purchase #7 $225.33   11.846%   $252.0226   $252.02   $252.00   $252.00  
  7 purchase totals = $789.23       $849.7527   $849.75   $849.75   $849.80