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 $204.43   13.723%   $232.4839   $232.48   $232.50   $232.50  
  Purchase #2 $96.90   10.579%   $107.1511   $107.15   $107.15   $107.20  
  Purchase #3 $180.37   11.625%   $201.338   $201.34   $201.35   $201.30  
  Purchase #4 $96.99   6.165%   $102.9694   $102.97   $102.95   $103.00  
  Purchase #5 $189.60   8.136%   $205.0259   $205.03   $205.05   $205.00  
  Purchase #6 $219.85   12.816%   $248.026   $248.03   $248.05   $248.00  
  Purchase #7 $238.62   6.434%   $253.9728   $253.97   $253.95   $254.00  
  7 purchase totals = $1,226.76       $1,350.9671   $1,350.97   $1,351.00   $1,351.00