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 $203.86   10.673%   $225.618   $225.62   $225.60   $225.60  
  Purchase #2 $205.95   3.152%   $212.4415   $212.44   $212.45   $212.40  
  Purchase #3 $170.39   3.380%   $176.1492   $176.15   $176.15   $176.10  
  Purchase #4 $219.80   7.241%   $235.7157   $235.72   $235.70   $235.70  
  Purchase #5 $76.73   11.598%   $85.6291   $85.63   $85.65   $85.60  
  Purchase #6 $39.85   10.136%   $43.8892   $43.89   $43.90   $43.90  
  Purchase #7 $218.76   13.347%   $247.9579   $247.96   $247.95   $248.00  
  7 purchase totals = $1,135.34       $1,227.4006   $1,227.41   $1,227.40   $1,227.30