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 $67.71   6.550%   $72.145   $72.15   $72.15   $72.10  
  Purchase #2 $247.56   10.833%   $274.3782   $274.38   $274.40   $274.40  
  Purchase #3 $86.87   11.625%   $96.9686   $96.97   $96.95   $97.00  
  Purchase #4 $81.44   7.590%   $87.6213   $87.62   $87.60   $87.60  
  Purchase #5 $248.91   11.713%   $278.0648   $278.06   $278.05   $278.10  
  Purchase #6 $48.93   8.418%   $53.0489   $53.05   $53.05   $53.00  
  Purchase #7 $197.40   4.467%   $206.2179   $206.22   $206.20   $206.20  
  7 purchase totals = $978.82       $1,068.4447   $1,068.45   $1,068.40   $1,068.40