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 $191.46   10.317%   $211.2129   $211.21   $211.20   $211.20  
  Purchase #2 $62.38   5.222%   $65.6375   $65.64   $65.65   $65.60  
  Purchase #3 $167.60   6.812%   $179.0169   $179.02   $179.00   $179.00  
  Purchase #4 $247.68   11.380%   $275.866   $275.87   $275.85   $275.90  
  Purchase #5 $104.59   11.630%   $116.7538   $116.75   $116.75   $116.80  
  Purchase #6 $11.29   8.631%   $12.2644   $12.26   $12.25   $12.30  
  Purchase #7 $228.32   9.494%   $249.9967   $250.00   $250.00   $250.00  
  7 purchase totals = $1,013.32       $1,110.7482   $1,110.75   $1,110.70   $1,110.80