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 $46.48   6.795%   $49.6383   $49.64   $49.65   $49.60  
  Purchase #2 $188.33   9.207%   $205.6695   $205.67   $205.65   $205.70  
  Purchase #3 $91.95   6.316%   $97.7576   $97.76   $97.75   $97.80  
  Purchase #4 $227.86   6.418%   $242.4841   $242.48   $242.50   $242.50  
  Purchase #5 $156.87   10.813%   $173.8324   $173.83   $173.85   $173.80  
  Purchase #6 $186.58   13.512%   $211.7907   $211.79   $211.80   $211.80  
  Purchase #7 $54.53   6.462%   $58.0537   $58.05   $58.05   $58.10  
  7 purchase totals = $952.60       $1,039.2263   $1,039.22   $1,039.25   $1,039.30