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 $31.28   10.834%   $34.6689   $34.67   $34.65   $34.70  
  Purchase #2 $229.62   11.867%   $256.869   $256.87   $256.85   $256.90  
  Purchase #3 $153.84   5.763%   $162.7058   $162.71   $162.70   $162.70  
  Purchase #4 $203.88   9.304%   $222.849   $222.85   $222.85   $222.80  
  Purchase #5 $65.51   13.262%   $74.1979   $74.20   $74.20   $74.20  
  Purchase #6 $22.91   11.425%   $25.5275   $25.53   $25.55   $25.50  
  Purchase #7 $114.38   9.337%   $125.0597   $125.06   $125.05   $125.10  
  7 purchase totals = $821.42       $901.8778   $901.89   $901.85   $901.90