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 $60.67   12.249%   $68.1015   $68.10   $68.10   $68.10  
  Purchase #2 $187.27   12.723%   $211.0964   $211.10   $211.10   $211.10  
  Purchase #3 $56.66   8.301%   $61.3633   $61.36   $61.35   $61.40  
  Purchase #4 $157.31   3.605%   $162.981   $162.98   $163.00   $163.00  
  Purchase #5 $53.55   3.667%   $55.5137   $55.51   $55.50   $55.50  
  Purchase #6 $78.51   4.728%   $82.222   $82.22   $82.20   $82.20  
  Purchase #7 $29.31   13.829%   $33.3633   $33.36   $33.35   $33.40  
  7 purchase totals = $623.28       $674.6412   $674.63   $674.60   $674.70