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 $145.95   12.156%   $163.6917   $163.69   $163.70   $163.70  
  Purchase #2 $162.98   9.652%   $178.7108   $178.71   $178.70   $178.70  
  Purchase #3 $22.49   4.836%   $23.5776   $23.58   $23.60   $23.60  
  Purchase #4 $213.51   10.148%   $235.177   $235.18   $235.20   $235.20  
  Purchase #5 $116.53   12.761%   $131.4004   $131.40   $131.40   $131.40  
  Purchase #6 $124.44   10.617%   $137.6518   $137.65   $137.65   $137.70  
  Purchase #7 $204.39   10.714%   $226.2883   $226.29   $226.30   $226.30  
  7 purchase totals = $990.29       $1,096.4976   $1,096.50   $1,096.55   $1,096.60