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 $93.26   5.413%   $98.3082   $98.31   $98.30   $98.30  
  Purchase #2 $65.27   8.322%   $70.7018   $70.70   $70.70   $70.70  
  Purchase #3 $5.68   4.125%   $5.9143   $5.91   $5.90   $5.90  
  Purchase #4 $87.99   11.284%   $97.9188   $97.92   $97.90   $97.90  
  Purchase #5 $211.34   8.494%   $229.2912   $229.29   $229.30   $229.30  
  Purchase #6 $200.98   10.796%   $222.6778   $222.68   $222.70   $222.70  
  Purchase #7 $28.70   4.699%   $30.0486   $30.05   $30.05   $30.00  
  7 purchase totals = $693.22       $754.8607   $754.86   $754.85   $754.80