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 $57.95   5.441%   $61.1031   $61.10   $61.10   $61.10  
  Purchase #2 $188.90   13.338%   $214.0955   $214.10   $214.10   $214.10  
  Purchase #3 $51.95   12.707%   $58.5513   $58.55   $58.55   $58.60  
  Purchase #4 $237.48   5.671%   $250.9475   $250.95   $250.95   $250.90  
  Purchase #5 $162.94   11.465%   $181.6211   $181.62   $181.60   $181.60  
  Purchase #6 $57.83   12.471%   $65.042   $65.04   $65.05   $65.00  
  Purchase #7 $51.30   4.611%   $53.6654   $53.67   $53.65   $53.70  
  7 purchase totals = $808.35       $885.0259   $885.03   $885.00   $885.00