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 $242.55   10.511%   $268.0444   $268.04   $268.05   $268.00  
  Purchase #2 $46.85   13.191%   $53.03   $53.03   $53.05   $53.00  
  Purchase #3 $172.90   5.593%   $182.5703   $182.57   $182.55   $182.60  
  Purchase #4 $167.54   13.793%   $190.6488   $190.65   $190.65   $190.60  
  Purchase #5 $178.82   13.644%   $203.2182   $203.22   $203.20   $203.20  
  Purchase #6 $221.36   9.505%   $242.4003   $242.40   $242.40   $242.40  
  Purchase #7 $88.58   6.228%   $94.0968   $94.10   $94.10   $94.10  
  7 purchase totals = $1,118.60       $1,234.0088   $1,234.01   $1,234.00   $1,233.90