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 $238.75   12.547%   $268.706   $268.71   $268.70   $268.70  
  Purchase #2 $60.94   3.113%   $62.8371   $62.84   $62.85   $62.80  
  Purchase #3 $88.87   9.707%   $97.4966   $97.50   $97.50   $97.50  
  Purchase #4 $219.34   12.825%   $247.4704   $247.47   $247.45   $247.50  
  Purchase #5 $163.31   13.677%   $185.6459   $185.65   $185.65   $185.60  
  Purchase #6 $210.94   7.605%   $226.982   $226.98   $227.00   $227.00  
  Purchase #7 $35.77   10.198%   $39.4178   $39.42   $39.40   $39.40  
  7 purchase totals = $1,017.92       $1,128.5558   $1,128.57   $1,128.55   $1,128.50