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 $80.54   6.787%   $86.0062   $86.01   $86.00   $86.00  
  Purchase #2 $101.92   7.232%   $109.2909   $109.29   $109.30   $109.30  
  Purchase #3 $147.62   7.854%   $159.2141   $159.21   $159.20   $159.20  
  Purchase #4 $214.40   6.429%   $228.1838   $228.18   $228.20   $228.20  
  Purchase #5 $18.74   3.585%   $19.4118   $19.41   $19.40   $19.40  
  Purchase #6 $241.59   5.664%   $255.2737   $255.27   $255.25   $255.30  
  Purchase #7 $187.96   11.148%   $208.9138   $208.91   $208.90   $208.90  
  7 purchase totals = $992.77       $1,066.2943   $1,066.28   $1,066.25   $1,066.30