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 $93.70   3.137%   $96.6394   $96.64   $96.65   $96.60  
  Purchase #2 $212.42   11.115%   $236.0305   $236.03   $236.05   $236.00  
  Purchase #3 $65.45   12.674%   $73.7451   $73.75   $73.75   $73.70  
  Purchase #4 $222.45   13.205%   $251.8245   $251.82   $251.80   $251.80  
  Purchase #5 $185.64   8.354%   $201.1484   $201.15   $201.15   $201.10  
  Purchase #6 $70.58   12.630%   $79.4943   $79.49   $79.50   $79.50  
  Purchase #7 $57.30   12.650%   $64.5485   $64.55   $64.55   $64.50  
  7 purchase totals = $907.54       $1,003.4307   $1,003.43   $1,003.45   $1,003.20