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 $49.36   9.854%   $54.2239   $54.22   $54.20   $54.20  
  Purchase #2 $246.50   11.280%   $274.3052   $274.31   $274.30   $274.30  
  Purchase #3 $148.34   9.291%   $162.1223   $162.12   $162.10   $162.10  
  Purchase #4 $204.66   13.682%   $232.6616   $232.66   $232.65   $232.70  
  Purchase #5 $110.47   3.176%   $113.9785   $113.98   $114.00   $114.00  
  Purchase #6 $153.60   8.733%   $167.0139   $167.01   $167.00   $167.00  
  Purchase #7 $240.30   12.268%   $269.78   $269.78   $269.80   $269.80  
  7 purchase totals = $1,153.23       $1,274.0854   $1,274.08   $1,274.05   $1,274.10