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 $14.62   13.250%   $16.5572   $16.56   $16.55   $16.60  
  Purchase #2 $236.93   4.215%   $246.9166   $246.92   $246.90   $246.90  
  Purchase #3 $203.41   11.708%   $227.2252   $227.23   $227.25   $227.20  
  Purchase #4 $228.58   6.871%   $244.2857   $244.29   $244.30   $244.30  
  Purchase #5 $203.95   7.392%   $219.026   $219.03   $219.05   $219.00  
  Purchase #6 $156.34   9.527%   $171.2345   $171.23   $171.25   $171.20  
  Purchase #7 $51.82   5.332%   $54.583   $54.58   $54.60   $54.60  
  7 purchase totals = $1,095.65       $1,179.8282   $1,179.84   $1,179.90   $1,179.80