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 $162.53   12.467%   $182.7926   $182.79   $182.80   $182.80  
  Purchase #2 $171.95   3.606%   $178.1505   $178.15   $178.15   $178.20  
  Purchase #3 $224.62   8.405%   $243.4993   $243.50   $243.50   $243.50  
  Purchase #4 $37.48   5.472%   $39.5309   $39.53   $39.55   $39.50  
  Purchase #5 $247.64   4.771%   $259.4549   $259.45   $259.45   $259.50  
  Purchase #6 $82.54   3.712%   $85.6039   $85.60   $85.60   $85.60  
  Purchase #7 $22.97   5.239%   $24.1734   $24.17   $24.15   $24.20  
  7 purchase totals = $949.73       $1,013.2055   $1,013.19   $1,013.20   $1,013.30