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 $245.35   13.149%   $277.6111   $277.61   $277.60   $277.60  
  Purchase #2 $154.50   11.575%   $172.3834   $172.38   $172.40   $172.40  
  Purchase #3 $68.90   8.658%   $74.8654   $74.87   $74.85   $74.90  
  Purchase #4 $182.39   10.745%   $201.9878   $201.99   $202.00   $202.00  
  Purchase #5 $216.59   13.448%   $245.717   $245.72   $245.70   $245.70  
  Purchase #6 $29.94   4.753%   $31.363   $31.36   $31.35   $31.40  
  Purchase #7 $73.72   11.803%   $82.4212   $82.42   $82.40   $82.40  
  7 purchase totals = $971.39       $1,086.3489   $1,086.35   $1,086.30   $1,086.40