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 $72.81   6.668%   $77.665   $77.67   $77.65   $77.70  
  Purchase #2 $31.44   3.690%   $32.6001   $32.60   $32.60   $32.60  
  Purchase #3 $119.96   5.608%   $126.6874   $126.69   $126.70   $126.70  
  Purchase #4 $198.84   5.431%   $209.639   $209.64   $209.65   $209.60  
  Purchase #5 $109.49   11.583%   $122.1722   $122.17   $122.15   $122.20  
  Purchase #6 $95.44   10.822%   $105.7685   $105.77   $105.75   $105.80  
  Purchase #7 $247.70   6.721%   $264.3479   $264.35   $264.35   $264.30  
  7 purchase totals = $875.68       $938.8801   $938.89   $938.85   $938.90