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 $141.57   10.776%   $156.8256   $156.83   $156.85   $156.80  
  Purchase #2 $184.81   9.461%   $202.2949   $202.29   $202.30   $202.30  
  Purchase #3 $195.59   8.355%   $211.9315   $211.93   $211.95   $211.90  
  Purchase #4 $102.55   5.272%   $107.9564   $107.96   $107.95   $108.00  
  Purchase #5 $29.99   8.608%   $32.5715   $32.57   $32.55   $32.60  
  Purchase #6 $158.46   3.806%   $164.491   $164.49   $164.50   $164.50  
  Purchase #7 $179.93   5.347%   $189.5509   $189.55   $189.55   $189.60  
  7 purchase totals = $992.90       $1,065.6218   $1,065.62   $1,065.65   $1,065.70