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 $25.58   5.641%   $27.023   $27.02   $27.00   $27.00  
  Purchase #2 $91.63   4.317%   $95.5857   $95.59   $95.60   $95.60  
  Purchase #3 $106.31   4.603%   $111.2034   $111.20   $111.20   $111.20  
  Purchase #4 $199.44   6.528%   $212.4594   $212.46   $212.45   $212.50  
  Purchase #5 $95.30   3.534%   $98.6679   $98.67   $98.65   $98.70  
  Purchase #6 $32.40   8.617%   $35.1919   $35.19   $35.20   $35.20  
  Purchase #7 $215.39   8.322%   $233.3148   $233.31   $233.30   $233.30  
  7 purchase totals = $766.05       $813.4461   $813.44   $813.40   $813.50