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 $173.39   13.674%   $197.0993   $197.10   $197.10   $197.10  
  Purchase #2 $155.60   6.682%   $165.9972   $166.00   $166.00   $166.00  
  Purchase #3 $36.26   12.167%   $40.6718   $40.67   $40.65   $40.70  
  Purchase #4 $22.70   6.494%   $24.1741   $24.17   $24.15   $24.20  
  Purchase #5 $71.75   7.336%   $77.0136   $77.01   $77.00   $77.00  
  Purchase #6 $239.28   10.864%   $265.2754   $265.28   $265.30   $265.30  
  Purchase #7 $173.47   6.815%   $185.292   $185.29   $185.30   $185.30  
  7 purchase totals = $872.45       $955.5234   $955.52   $955.50   $955.60