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 $150.97   7.724%   $162.6309   $162.63   $162.65   $162.60  
  Purchase #2 $40.59   3.452%   $41.9912   $41.99   $42.00   $42.00  
  Purchase #3 $206.58   6.564%   $220.1399   $220.14   $220.15   $220.10  
  Purchase #4 $88.31   13.278%   $100.0358   $100.04   $100.05   $100.00  
  Purchase #5 $7.33   11.637%   $8.183   $8.18   $8.20   $8.20  
  Purchase #6 $64.51   8.630%   $70.0772   $70.08   $70.10   $70.10  
  Purchase #7 $78.32   11.550%   $87.366   $87.37   $87.35   $87.40  
  7 purchase totals = $636.61       $690.4240   $690.43   $690.50   $690.40