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 $65.95   6.262%   $70.0798   $70.08   $70.10   $70.10  
  Purchase #2 $223.33   11.778%   $249.6338   $249.63   $249.65   $249.60  
  Purchase #3 $92.89   7.757%   $100.0955   $100.10   $100.10   $100.10  
  Purchase #4 $44.85   7.774%   $48.3366   $48.34   $48.35   $48.30  
  Purchase #5 $153.86   9.795%   $168.9306   $168.93   $168.95   $168.90  
  Purchase #6 $121.27   5.426%   $127.8501   $127.85   $127.85   $127.90  
  Purchase #7 $111.84   9.799%   $122.7992   $122.80   $122.80   $122.80  
  7 purchase totals = $813.99       $887.7256   $887.73   $887.80   $887.70