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 $236.49   9.254%   $258.3748   $258.37   $258.35   $258.40  
  Purchase #2 $179.46   12.348%   $201.6197   $201.62   $201.60   $201.60  
  Purchase #3 $32.49   12.660%   $36.6032   $36.60   $36.60   $36.60  
  Purchase #4 $81.87   4.204%   $85.3118   $85.31   $85.30   $85.30  
  Purchase #5 $96.34   8.410%   $104.4422   $104.44   $104.45   $104.40  
  Purchase #6 $154.27   13.321%   $174.8203   $174.82   $174.80   $174.80  
  Purchase #7 $22.46   9.420%   $24.5757   $24.58   $24.60   $24.60  
  7 purchase totals = $803.38       $885.7477   $885.74   $885.70   $885.70