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 $34.61   11.740%   $38.6732   $38.67   $38.65   $38.70  
  Purchase #2 $64.74   3.163%   $66.7877   $66.79   $66.80   $66.80  
  Purchase #3 $23.29   3.751%   $24.1636   $24.16   $24.15   $24.20  
  Purchase #4 $57.84   3.649%   $59.9506   $59.95   $59.95   $60.00  
  Purchase #5 $230.80   9.711%   $253.213   $253.21   $253.20   $253.20  
  Purchase #6 $116.90   8.637%   $126.9967   $127.00   $127.00   $127.00  
  Purchase #7 $162.32   12.153%   $182.0467   $182.05   $182.05   $182.00  
  7 purchase totals = $690.50       $751.8315   $751.83   $751.80   $751.90