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 $57.95   12.207%   $65.024   $65.02   $65.00   $65.00  
  Purchase #2 $170.65   9.420%   $186.7252   $186.73   $186.75   $186.70  
  Purchase #3 $122.92   7.247%   $131.828   $131.83   $131.85   $131.80  
  Purchase #4 $93.77   11.232%   $104.3022   $104.30   $104.30   $104.30  
  Purchase #5 $161.41   13.529%   $183.2472   $183.25   $183.25   $183.20  
  Purchase #6 $202.51   8.435%   $219.5917   $219.59   $219.60   $219.60  
  Purchase #7 $136.85   8.170%   $148.0306   $148.03   $148.05   $148.00  
  7 purchase totals = $946.06       $1,038.7489   $1,038.75   $1,038.80   $1,038.60