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 $223.82   10.443%   $247.1935   $247.19   $247.20   $247.20  
  Purchase #2 $192.84   5.246%   $202.9564   $202.96   $202.95   $203.00  
  Purchase #3 $138.60   11.766%   $154.9077   $154.91   $154.90   $154.90  
  Purchase #4 $219.32   7.143%   $234.986   $234.99   $235.00   $235.00  
  Purchase #5 $148.52   8.683%   $161.416   $161.42   $161.40   $161.40  
  Purchase #6 $9.60   5.591%   $10.1367   $10.14   $10.15   $10.10  
  Purchase #7 $108.62   7.732%   $117.0185   $117.02   $117.00   $117.00  
  7 purchase totals = $1,041.32       $1,128.6148   $1,128.63   $1,128.60   $1,128.60