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 $60.60   9.296%   $66.2334   $66.23   $66.25   $66.20  
  Purchase #2 $205.25   8.353%   $222.3945   $222.39   $222.40   $222.40  
  Purchase #3 $202.58   11.676%   $226.2332   $226.23   $226.25   $226.20  
  Purchase #4 $79.45   3.502%   $82.2323   $82.23   $82.25   $82.20  
  Purchase #5 $163.68   9.770%   $179.6715   $179.67   $179.65   $179.70  
  Purchase #6 $208.95   3.726%   $216.7355   $216.74   $216.75   $216.70  
  Purchase #7 $22.54   11.648%   $25.1655   $25.17   $25.15   $25.20  
  7 purchase totals = $943.05       $1,018.6659   $1,018.66   $1,018.70   $1,018.60