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 $62.30   13.152%   $70.4937   $70.49   $70.50   $70.50  
  Purchase #2 $57.76   11.655%   $64.4919   $64.49   $64.50   $64.50  
  Purchase #3 $189.82   7.331%   $203.7357   $203.74   $203.75   $203.70  
  Purchase #4 $62.42   12.425%   $70.1757   $70.18   $70.20   $70.20  
  Purchase #5 $86.34   6.429%   $91.8908   $91.89   $91.90   $91.90  
  Purchase #6 $204.49   6.609%   $218.0047   $218.00   $218.00   $218.00  
  Purchase #7 $40.86   6.433%   $43.4885   $43.49   $43.50   $43.50  
  7 purchase totals = $703.99       $762.2810   $762.28   $762.35   $762.30