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 $243.37   11.465%   $271.2724   $271.27   $271.25   $271.30  
  Purchase #2 $204.29   9.639%   $223.9815   $223.98   $224.00   $224.00  
  Purchase #3 $174.32   13.591%   $198.0118   $198.01   $198.00   $198.00  
  Purchase #4 $151.85   9.864%   $166.8285   $166.83   $166.85   $166.80  
  Purchase #5 $187.76   9.587%   $205.7606   $205.76   $205.75   $205.80  
  Purchase #6 $249.56   8.605%   $271.0346   $271.03   $271.05   $271.00  
  Purchase #7 $163.25   10.610%   $180.5708   $180.57   $180.55   $180.60  
  7 purchase totals = $1,374.40       $1,517.4602   $1,517.45   $1,517.45   $1,517.50