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 $51.39   4.277%   $53.588   $53.59   $53.60   $53.60  
  Purchase #2 $91.98   3.803%   $95.478   $95.48   $95.50   $95.50  
  Purchase #3 $207.45   10.694%   $229.6347   $229.63   $229.65   $229.60  
  Purchase #4 $181.47   9.405%   $198.5373   $198.54   $198.55   $198.50  
  Purchase #5 $21.87   7.335%   $23.4742   $23.47   $23.45   $23.50  
  Purchase #6 $223.31   11.805%   $249.6717   $249.67   $249.65   $249.70  
  Purchase #7 $77.84   8.728%   $84.6339   $84.63   $84.65   $84.60  
  7 purchase totals = $855.31       $935.0178   $935.01   $935.05   $935.00