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 $61.84   6.243%   $65.7007   $65.70   $65.70   $65.70  
  Purchase #2 $77.99   8.522%   $84.6363   $84.64   $84.65   $84.60  
  Purchase #3 $132.79   11.617%   $148.2162   $148.22   $148.20   $148.20  
  Purchase #4 $140.75   6.721%   $150.2098   $150.21   $150.20   $150.20  
  Purchase #5 $208.63   8.296%   $225.9379   $225.94   $225.95   $225.90  
  Purchase #6 $246.52   9.817%   $270.7209   $270.72   $270.70   $270.70  
  Purchase #7 $112.55   13.716%   $127.9874   $127.99   $128.00   $128.00  
  7 purchase totals = $981.07       $1,073.4092   $1,073.42   $1,073.40   $1,073.30