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 $96.53   8.504%   $104.7389   $104.74   $104.75   $104.70  
  Purchase #2 $201.44   13.116%   $227.8609   $227.86   $227.85   $227.90  
  Purchase #3 $235.50   8.681%   $255.9438   $255.94   $255.95   $255.90  
  Purchase #4 $59.87   3.292%   $61.8409   $61.84   $61.85   $61.80  
  Purchase #5 $74.94   3.607%   $77.6431   $77.64   $77.65   $77.60  
  Purchase #6 $184.77   9.253%   $201.8668   $201.87   $201.85   $201.90  
  Purchase #7 $154.88   3.866%   $160.8677   $160.87   $160.85   $160.90  
  7 purchase totals = $1,007.93       $1,090.7621   $1,090.76   $1,090.75   $1,090.70