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 $192.57   10.418%   $212.6319   $212.63   $212.65   $212.60  
  Purchase #2 $113.80   11.359%   $126.7265   $126.73   $126.75   $126.70  
  Purchase #3 $185.44   6.342%   $197.2006   $197.20   $197.20   $197.20  
  Purchase #4 $194.47   3.540%   $201.3542   $201.35   $201.35   $201.40  
  Purchase #5 $95.67   8.806%   $104.0947   $104.09   $104.10   $104.10  
  Purchase #6 $135.44   6.769%   $144.6079   $144.61   $144.60   $144.60  
  Purchase #7 $21.59   10.864%   $23.9355   $23.94   $23.95   $23.90  
  7 purchase totals = $938.98       $1,010.5513   $1,010.55   $1,010.60   $1,010.50