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 $57.76   6.818%   $61.6981   $61.70   $61.70   $61.70  
  Purchase #2 $170.62   13.556%   $193.7492   $193.75   $193.75   $193.70  
  Purchase #3 $56.50   13.527%   $64.1428   $64.14   $64.15   $64.10  
  Purchase #4 $158.35   9.721%   $173.7432   $173.74   $173.75   $173.70  
  Purchase #5 $123.41   8.689%   $134.1331   $134.13   $134.15   $134.10  
  Purchase #6 $136.65   4.814%   $143.2283   $143.23   $143.25   $143.20  
  Purchase #7 $234.95   8.355%   $254.5801   $254.58   $254.60   $254.60  
  7 purchase totals = $938.24       $1,025.2748   $1,025.27   $1,025.35   $1,025.10