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 $82.64   12.770%   $93.1931   $93.19   $93.20   $93.20  
  Purchase #2 $57.75   4.152%   $60.1478   $60.15   $60.15   $60.10  
  Purchase #3 $82.37   3.482%   $85.2381   $85.24   $85.25   $85.20  
  Purchase #4 $236.61   8.629%   $257.0271   $257.03   $257.05   $257.00  
  Purchase #5 $144.37   5.735%   $152.6496   $152.65   $152.65   $152.60  
  Purchase #6 $234.98   9.813%   $258.0386   $258.04   $258.05   $258.00  
  Purchase #7 $118.65   3.431%   $122.7209   $122.72   $122.70   $122.70  
  7 purchase totals = $957.37       $1,029.0152   $1,029.02   $1,029.05   $1,028.80