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 $250.82   6.433%   $266.9553   $266.96   $266.95   $267.00  
  Purchase #2 $189.82   12.801%   $214.1189   $214.12   $214.10   $214.10  
  Purchase #3 $134.39   4.759%   $140.7856   $140.79   $140.80   $140.80  
  Purchase #4 $33.61   7.452%   $36.1146   $36.11   $36.10   $36.10  
  Purchase #5 $13.67   4.662%   $14.3073   $14.31   $14.30   $14.30  
  Purchase #6 $224.80   13.264%   $254.6175   $254.62   $254.60   $254.60  
  Purchase #7 $177.81   12.408%   $199.8727   $199.87   $199.85   $199.90  
  7 purchase totals = $1,024.92       $1,126.7719   $1,126.78   $1,126.70   $1,126.80