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 $205.45   9.541%   $225.052   $225.05   $225.05   $225.10  
  Purchase #2 $65.75   10.186%   $72.4473   $72.45   $72.45   $72.40  
  Purchase #3 $203.97   3.449%   $211.0049   $211.00   $211.00   $211.00  
  Purchase #4 $88.69   12.202%   $99.512   $99.51   $99.50   $99.50  
  Purchase #5 $34.72   7.185%   $37.2146   $37.21   $37.20   $37.20  
  Purchase #6 $130.40   6.494%   $138.8682   $138.87   $138.85   $138.90  
  Purchase #7 $161.77   3.313%   $167.1294   $167.13   $167.15   $167.10  
  7 purchase totals = $890.75       $951.2284   $951.22   $951.20   $951.20