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 $162.44   7.122%   $174.009   $174.01   $174.00   $174.00  
  Purchase #2 $74.87   3.212%   $77.2748   $77.27   $77.25   $77.30  
  Purchase #3 $28.35   7.670%   $30.5244   $30.52   $30.50   $30.50  
  Purchase #4 $95.62   9.696%   $104.8913   $104.89   $104.90   $104.90  
  Purchase #5 $179.36   6.587%   $191.1744   $191.17   $191.15   $191.20  
  Purchase #6 $157.41   6.668%   $167.9061   $167.91   $167.90   $167.90  
  Purchase #7 $51.98   5.422%   $54.7984   $54.80   $54.80   $54.80  
  7 purchase totals = $750.03       $800.5784   $800.57   $800.50   $800.60