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 $51.47   5.270%   $54.1825   $54.18   $54.20   $54.20  
  Purchase #2 $11.66   4.580%   $12.194   $12.19   $12.20   $12.20  
  Purchase #3 $75.51   12.791%   $85.1685   $85.17   $85.15   $85.20  
  Purchase #4 $114.63   9.415%   $125.4224   $125.42   $125.40   $125.40  
  Purchase #5 $214.93   11.231%   $239.0688   $239.07   $239.05   $239.10  
  Purchase #6 $147.46   4.838%   $154.5941   $154.59   $154.60   $154.60  
  Purchase #7 $89.45   7.296%   $95.9763   $95.98   $96.00   $96.00  
  7 purchase totals = $705.11       $766.6066   $766.60   $766.60   $766.70