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 $169.26   12.166%   $189.8522   $189.85   $189.85   $189.90  
  Purchase #2 $18.50   11.280%   $20.5868   $20.59   $20.60   $20.60  
  Purchase #3 $237.95   6.153%   $252.5911   $252.59   $252.60   $252.60  
  Purchase #4 $170.33   7.408%   $182.948   $182.95   $182.95   $182.90  
  Purchase #5 $205.95   12.725%   $232.1571   $232.16   $232.15   $232.20  
  Purchase #6 $42.55   10.403%   $46.9765   $46.98   $47.00   $47.00  
  Purchase #7 $182.41   4.726%   $191.0307   $191.03   $191.05   $191.00  
  7 purchase totals = $1,026.95       $1,116.1424   $1,116.15   $1,116.20   $1,116.20