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 $214.52   12.698%   $241.7597   $241.76   $241.75   $241.80  
  Purchase #2 $222.99   12.222%   $250.2438   $250.24   $250.25   $250.20  
  Purchase #3 $51.46   12.193%   $57.7345   $57.73   $57.75   $57.70  
  Purchase #4 $51.40   12.810%   $57.9843   $57.98   $58.00   $58.00  
  Purchase #5 $162.47   7.714%   $175.0029   $175.00   $175.00   $175.00  
  Purchase #6 $151.65   5.738%   $160.3517   $160.35   $160.35   $160.40  
  Purchase #7 $56.95   10.260%   $62.7931   $62.79   $62.80   $62.80  
  7 purchase totals = $911.44       $1,005.8700   $1,005.85   $1,005.90   $1,005.90