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 $97.29   7.216%   $104.3104   $104.31   $104.30   $104.30  
  Purchase #2 $87.65   8.745%   $95.315   $95.32   $95.30   $95.30  
  Purchase #3 $114.97   12.374%   $129.1964   $129.20   $129.20   $129.20  
  Purchase #4 $161.72   10.398%   $178.5356   $178.54   $178.55   $178.50  
  Purchase #5 $161.91   10.144%   $178.3342   $178.33   $178.35   $178.30  
  Purchase #6 $133.31   5.521%   $140.67   $140.67   $140.65   $140.70  
  Purchase #7 $200.38   6.540%   $213.4849   $213.48   $213.50   $213.50  
  7 purchase totals = $957.23       $1,039.8465   $1,039.85   $1,039.85   $1,039.80