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 $164.63   12.216%   $184.7412   $184.74   $184.75   $184.70  
  Purchase #2 $134.46   5.367%   $141.6765   $141.68   $141.70   $141.70  
  Purchase #3 $149.94   9.652%   $164.4122   $164.41   $164.40   $164.40  
  Purchase #4 $153.28   10.340%   $169.1292   $169.13   $169.15   $169.10  
  Purchase #5 $8.80   4.506%   $9.1965   $9.20   $9.20   $9.20  
  Purchase #6 $223.59   9.535%   $244.9093   $244.91   $244.90   $244.90  
  Purchase #7 $96.81   11.522%   $107.9644   $107.96   $107.95   $108.00  
  7 purchase totals = $931.51       $1,022.0293   $1,022.03   $1,022.05   $1,022.00