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 $228.29   10.527%   $252.3221   $252.32   $252.30   $252.30  
  Purchase #2 $194.82   13.256%   $220.6453   $220.65   $220.65   $220.60  
  Purchase #3 $127.56   4.482%   $133.2772   $133.28   $133.30   $133.30  
  Purchase #4 $151.33   5.143%   $159.1129   $159.11   $159.10   $159.10  
  Purchase #5 $73.74   4.561%   $77.1033   $77.10   $77.10   $77.10  
  Purchase #6 $153.48   5.776%   $162.345   $162.35   $162.35   $162.30  
  Purchase #7 $183.37   9.461%   $200.7186   $200.72   $200.70   $200.70  
  7 purchase totals = $1,112.59       $1,205.5244   $1,205.53   $1,205.50   $1,205.40