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 $249.49   13.741%   $283.7724   $283.77   $283.75   $283.80  
  Purchase #2 $231.35   12.547%   $260.3775   $260.38   $260.40   $260.40  
  Purchase #3 $69.32   10.569%   $76.6464   $76.65   $76.65   $76.60  
  Purchase #4 $9.94   9.273%   $10.8617   $10.86   $10.85   $10.90  
  Purchase #5 $25.47   6.868%   $27.2193   $27.22   $27.20   $27.20  
  Purchase #6 $242.54   9.383%   $265.2975   $265.30   $265.30   $265.30  
  Purchase #7 $98.46   10.102%   $108.4064   $108.41   $108.40   $108.40  
  7 purchase totals = $926.57       $1,032.5812   $1,032.59   $1,032.55   $1,032.60