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 $118.49   4.255%   $123.5317   $123.53   $123.55   $123.50  
  Purchase #2 $125.33   10.584%   $138.5949   $138.59   $138.60   $138.60  
  Purchase #3 $248.34   13.516%   $281.9056   $281.91   $281.90   $281.90  
  Purchase #4 $188.55   12.305%   $211.7511   $211.75   $211.75   $211.80  
  Purchase #5 $204.75   13.276%   $231.9326   $231.93   $231.95   $231.90  
  Purchase #6 $8.95   4.313%   $9.336   $9.34   $9.35   $9.30  
  Purchase #7 $13.50   13.400%   $15.309   $15.31   $15.30   $15.30  
  7 purchase totals = $907.91       $1,012.3609   $1,012.36   $1,012.40   $1,012.30