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 $92.43   5.703%   $97.7013   $97.70   $97.70   $97.70  
  Purchase #2 $214.91   12.603%   $241.9951   $242.00   $242.00   $242.00  
  Purchase #3 $15.79   10.708%   $17.4808   $17.48   $17.50   $17.50  
  Purchase #4 $193.36   5.254%   $203.5191   $203.52   $203.50   $203.50  
  Purchase #5 $217.59   11.268%   $242.108   $242.11   $242.10   $242.10  
  Purchase #6 $127.93   3.225%   $132.0557   $132.06   $132.05   $132.10  
  Purchase #7 $54.83   5.838%   $58.031   $58.03   $58.05   $58.00  
  7 purchase totals = $916.84       $992.8910   $992.90   $992.90   $992.90