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 $31.66   11.172%   $35.1971   $35.20   $35.20   $35.20  
  Purchase #2 $164.59   12.738%   $185.5555   $185.56   $185.55   $185.60  
  Purchase #3 $124.58   10.335%   $137.4553   $137.46   $137.45   $137.50  
  Purchase #4 $196.61   3.511%   $203.513   $203.51   $203.50   $203.50  
  Purchase #5 $67.36   5.861%   $71.308   $71.31   $71.30   $71.30  
  Purchase #6 $57.49   12.744%   $64.8165   $64.82   $64.80   $64.80  
  Purchase #7 $184.74   10.317%   $203.7996   $203.80   $203.80   $203.80  
  7 purchase totals = $827.03       $901.6450   $901.66   $901.60   $901.70