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 $152.57   7.398%   $163.8571   $163.86   $163.85   $163.90  
  Purchase #2 $240.41   4.521%   $251.2789   $251.28   $251.30   $251.30  
  Purchase #3 $216.76   13.761%   $246.5883   $246.59   $246.60   $246.60  
  Purchase #4 $16.93   11.581%   $18.8907   $18.89   $18.90   $18.90  
  Purchase #5 $66.92   12.230%   $75.1043   $75.10   $75.10   $75.10  
  Purchase #6 $20.97   12.656%   $23.624   $23.62   $23.60   $23.60  
  Purchase #7 $204.94   11.537%   $228.5839   $228.58   $228.60   $228.60  
  7 purchase totals = $919.50       $1,007.9272   $1,007.92   $1,007.95   $1,008.00