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 $201.74   8.335%   $218.555   $218.56   $218.55   $218.60  
  Purchase #2 $47.64   8.370%   $51.6275   $51.63   $51.65   $51.60  
  Purchase #3 $99.79   8.404%   $108.1764   $108.18   $108.20   $108.20  
  Purchase #4 $227.84   3.439%   $235.6754   $235.68   $235.70   $235.70  
  Purchase #5 $244.75   12.619%   $275.635   $275.64   $275.65   $275.60  
  Purchase #6 $215.88   4.714%   $226.0566   $226.06   $226.05   $226.10  
  Purchase #7 $73.97   8.699%   $80.4047   $80.40   $80.40   $80.40  
  7 purchase totals = $1,111.61       $1,196.1306   $1,196.15   $1,196.20   $1,196.20