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 $212.34   11.231%   $236.1879   $236.19   $236.20   $236.20  
  Purchase #2 $167.26   12.753%   $188.5907   $188.59   $188.60   $188.60  
  Purchase #3 $36.50   12.253%   $40.9723   $40.97   $40.95   $41.00  
  Purchase #4 $85.93   11.517%   $95.8266   $95.83   $95.85   $95.80  
  Purchase #5 $207.29   3.752%   $215.0675   $215.07   $215.05   $215.10  
  Purchase #6 $72.37   9.349%   $79.1359   $79.14   $79.15   $79.10  
  Purchase #7 $148.32   4.631%   $155.1887   $155.19   $155.20   $155.20  
  7 purchase totals = $930.01       $1,010.9696   $1,010.98   $1,011.00   $1,011.00