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 $55.68   6.112%   $59.0832   $59.08   $59.10   $59.10  
  Purchase #2 $128.38   6.758%   $137.0559   $137.06   $137.05   $137.10  
  Purchase #3 $22.67   11.751%   $25.334   $25.33   $25.35   $25.30  
  Purchase #4 $117.42   6.724%   $125.3153   $125.32   $125.30   $125.30  
  Purchase #5 $12.28   9.133%   $13.4015   $13.40   $13.40   $13.40  
  Purchase #6 $164.83   11.464%   $183.7261   $183.73   $183.75   $183.70  
  Purchase #7 $114.67   12.536%   $129.045   $129.05   $129.05   $129.00  
  7 purchase totals = $615.93       $672.9610   $672.97   $673.00   $672.90