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 $61.66   3.522%   $63.8317   $63.83   $63.85   $63.80  
  Purchase #2 $173.41   11.377%   $193.1389   $193.14   $193.15   $193.10  
  Purchase #3 $166.28   4.776%   $174.2215   $174.22   $174.20   $174.20  
  Purchase #4 $201.53   13.151%   $228.0332   $228.03   $228.05   $228.00  
  Purchase #5 $244.80   7.421%   $262.9666   $262.97   $262.95   $263.00  
  Purchase #6 $81.92   12.524%   $92.1797   $92.18   $92.20   $92.20  
  Purchase #7 $25.62   8.315%   $27.7503   $27.75   $27.75   $27.80  
  7 purchase totals = $955.22       $1,042.1219   $1,042.12   $1,042.15   $1,042.10