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 $163.27   11.770%   $182.4869   $182.49   $182.50   $182.50  
  Purchase #2 $53.79   7.469%   $57.8076   $57.81   $57.80   $57.80  
  Purchase #3 $243.99   13.647%   $277.2873   $277.29   $277.30   $277.30  
  Purchase #4 $239.63   8.587%   $260.207   $260.21   $260.20   $260.20  
  Purchase #5 $79.50   6.260%   $84.4767   $84.48   $84.50   $84.50  
  Purchase #6 $223.49   10.596%   $247.171   $247.17   $247.15   $247.20  
  Purchase #7 $240.85   10.501%   $266.1417   $266.14   $266.15   $266.10  
  7 purchase totals = $1,244.52       $1,375.5782   $1,375.59   $1,375.60   $1,375.60