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 $96.59   5.358%   $101.7653   $101.77   $101.75   $101.80  
  Purchase #2 $76.46   7.304%   $82.0446   $82.04   $82.05   $82.00  
  Purchase #3 $216.75   5.743%   $229.198   $229.20   $229.20   $229.20  
  Purchase #4 $15.62   13.782%   $17.7727   $17.77   $17.75   $17.80  
  Purchase #5 $202.29   4.411%   $211.213   $211.21   $211.20   $211.20  
  Purchase #6 $151.89   10.505%   $167.846   $167.85   $167.85   $167.80  
  Purchase #7 $131.97   11.530%   $147.1861   $147.19   $147.20   $147.20  
  7 purchase totals = $891.57       $957.0257   $957.03   $957.00   $957.00