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 $45.29   5.773%   $47.9046   $47.90   $47.90   $47.90  
  Purchase #2 $101.95   5.235%   $107.2871   $107.29   $107.30   $107.30  
  Purchase #3 $246.40   8.566%   $267.5066   $267.51   $267.50   $267.50  
  Purchase #4 $56.93   10.663%   $63.0004   $63.00   $63.00   $63.00  
  Purchase #5 $170.54   12.155%   $191.2691   $191.27   $191.25   $191.30  
  Purchase #6 $221.98   5.752%   $234.7483   $234.75   $234.75   $234.70  
  Purchase #7 $185.72   3.563%   $192.3372   $192.34   $192.35   $192.30  
  7 purchase totals = $1,028.81       $1,104.0533   $1,104.06   $1,104.05   $1,104.00