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 $241.86   6.823%   $258.3621   $258.36   $258.35   $258.40  
  Purchase #2 $228.87   4.184%   $238.4459   $238.45   $238.45   $238.40  
  Purchase #3 $193.58   11.721%   $216.2695   $216.27   $216.25   $216.30  
  Purchase #4 $213.49   5.736%   $225.7358   $225.74   $225.75   $225.70  
  Purchase #5 $182.94   11.132%   $203.3049   $203.30   $203.30   $203.30  
  Purchase #6 $239.32   7.846%   $258.097   $258.10   $258.10   $258.10  
  Purchase #7 $13.58   7.187%   $14.556   $14.56   $14.55   $14.60  
  7 purchase totals = $1,313.64       $1,414.7712   $1,414.78   $1,414.75   $1,414.80