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 $169.94   7.375%   $182.4731   $182.47   $182.45   $182.50  
  Purchase #2 $44.77   9.843%   $49.1767   $49.18   $49.20   $49.20  
  Purchase #3 $92.55   5.263%   $97.4209   $97.42   $97.40   $97.40  
  Purchase #4 $195.64   4.229%   $203.9136   $203.91   $203.90   $203.90  
  Purchase #5 $187.47   6.467%   $199.5937   $199.59   $199.60   $199.60  
  Purchase #6 $203.63   6.222%   $216.2999   $216.30   $216.30   $216.30  
  Purchase #7 $223.47   9.467%   $244.6259   $244.63   $244.65   $244.60  
  7 purchase totals = $1,117.47       $1,193.5038   $1,193.50   $1,193.50   $1,193.50