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 $100.64   12.133%   $112.8507   $112.85   $112.85   $112.90  
  Purchase #2 $159.57   8.645%   $173.3648   $173.36   $173.35   $173.40  
  Purchase #3 $172.66   12.501%   $194.2442   $194.24   $194.25   $194.20  
  Purchase #4 $194.48   13.434%   $220.6064   $220.61   $220.60   $220.60  
  Purchase #5 $18.91   12.758%   $21.3225   $21.32   $21.30   $21.30  
  Purchase #6 $194.75   6.606%   $207.6152   $207.62   $207.60   $207.60  
  Purchase #7 $92.57   9.215%   $101.1003   $101.10   $101.10   $101.10  
  7 purchase totals = $933.58       $1,031.1041   $1,031.10   $1,031.05   $1,031.10