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 $240.86   10.682%   $266.5887   $266.59   $266.60   $266.60  
  Purchase #2 $213.31   11.309%   $237.4332   $237.43   $237.45   $237.40  
  Purchase #3 $50.27   6.303%   $53.4385   $53.44   $53.45   $53.40  
  Purchase #4 $194.39   5.214%   $204.5255   $204.53   $204.55   $204.50  
  Purchase #5 $97.34   6.866%   $104.0234   $104.02   $104.00   $104.00  
  Purchase #6 $153.50   9.260%   $167.7141   $167.71   $167.70   $167.70  
  Purchase #7 $90.30   3.444%   $93.4099   $93.41   $93.40   $93.40  
  7 purchase totals = $1,039.97       $1,127.1333   $1,127.13   $1,127.15   $1,127.00