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 $62.88   4.862%   $65.9372   $65.94   $65.95   $65.90  
  Purchase #2 $114.57   9.713%   $125.6982   $125.70   $125.70   $125.70  
  Purchase #3 $66.64   13.502%   $75.6377   $75.64   $75.65   $75.60  
  Purchase #4 $58.92   6.537%   $62.7716   $62.77   $62.75   $62.80  
  Purchase #5 $87.30   10.815%   $96.7415   $96.74   $96.75   $96.70  
  Purchase #6 $198.85   9.125%   $216.9951   $217.00   $217.00   $217.00  
  Purchase #7 $30.72   10.574%   $33.9683   $33.97   $33.95   $34.00  
  7 purchase totals = $619.88       $677.7496   $677.76   $677.75   $677.70