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 $136.45   8.171%   $147.5993   $147.60   $147.60   $147.60  
  Purchase #2 $151.96   11.110%   $168.8428   $168.84   $168.85   $168.80  
  Purchase #3 $114.59   3.537%   $118.643   $118.64   $118.65   $118.60  
  Purchase #4 $155.64   9.298%   $170.1114   $170.11   $170.10   $170.10  
  Purchase #5 $174.25   9.657%   $191.0773   $191.08   $191.10   $191.10  
  Purchase #6 $46.98   12.553%   $52.8774   $52.88   $52.90   $52.90  
  Purchase #7 $139.25   5.185%   $146.4701   $146.47   $146.45   $146.50  
  7 purchase totals = $919.12       $995.6213   $995.62   $995.65   $995.60