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 $69.29   8.759%   $75.3591   $75.36   $75.35   $75.40  
  Purchase #2 $146.30   9.258%   $159.8445   $159.84   $159.85   $159.80  
  Purchase #3 $143.69   13.154%   $162.591   $162.59   $162.60   $162.60  
  Purchase #4 $250.95   9.661%   $275.1943   $275.19   $275.20   $275.20  
  Purchase #5 $165.60   6.572%   $176.4832   $176.48   $176.50   $176.50  
  Purchase #6 $48.78   5.806%   $51.6122   $51.61   $51.60   $51.60  
  Purchase #7 $75.70   8.603%   $82.2125   $82.21   $82.20   $82.20  
  7 purchase totals = $900.31       $983.2968   $983.28   $983.30   $983.30