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 $233.51   13.285%   $264.5318   $264.53   $264.55   $264.50  
  Purchase #2 $44.44   10.799%   $49.2391   $49.24   $49.25   $49.20  
  Purchase #3 $195.96   12.618%   $220.6862   $220.69   $220.70   $220.70  
  Purchase #4 $228.67   9.351%   $250.0529   $250.05   $250.05   $250.10  
  Purchase #5 $30.40   12.237%   $34.12   $34.12   $34.10   $34.10  
  Purchase #6 $206.30   4.297%   $215.1647   $215.16   $215.15   $215.20  
  Purchase #7 $24.60   6.104%   $26.1016   $26.10   $26.10   $26.10  
  7 purchase totals = $963.88       $1,059.8963   $1,059.89   $1,059.90   $1,059.90