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 $212.42   11.508%   $236.8653   $236.87   $236.85   $236.90  
  Purchase #2 $168.81   10.324%   $186.2379   $186.24   $186.25   $186.20  
  Purchase #3 $247.80   6.200%   $263.1636   $263.16   $263.15   $263.20  
  Purchase #4 $57.94   10.666%   $64.1199   $64.12   $64.10   $64.10  
  Purchase #5 $59.60   5.494%   $62.8744   $62.87   $62.85   $62.90  
  Purchase #6 $50.73   12.676%   $57.1605   $57.16   $57.15   $57.20  
  Purchase #7 $119.94   12.796%   $135.2875   $135.29   $135.30   $135.30  
  7 purchase totals = $917.24       $1,005.7091   $1,005.71   $1,005.65   $1,005.80