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 $76.87   11.795%   $85.9368   $85.94   $85.95   $85.90  
  Purchase #2 $59.41   4.853%   $62.2932   $62.29   $62.30   $62.30  
  Purchase #3 $208.91   10.575%   $231.0022   $231.00   $231.00   $231.00  
  Purchase #4 $123.84   3.856%   $128.6153   $128.62   $128.60   $128.60  
  Purchase #5 $33.85   11.256%   $37.6602   $37.66   $37.65   $37.70  
  Purchase #6 $178.49   13.814%   $203.1466   $203.15   $203.15   $203.10  
  Purchase #7 $103.57   10.148%   $114.0803   $114.08   $114.10   $114.10  
  7 purchase totals = $784.94       $862.7346   $862.74   $862.75   $862.70