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 $192.57   7.118%   $206.2771   $206.28   $206.30   $206.30  
  Purchase #2 $101.60   11.858%   $113.6477   $113.65   $113.65   $113.60  
  Purchase #3 $196.87   6.808%   $210.2729   $210.27   $210.25   $210.30  
  Purchase #4 $239.68   9.560%   $262.5934   $262.59   $262.60   $262.60  
  Purchase #5 $126.56   12.704%   $142.6382   $142.64   $142.65   $142.60  
  Purchase #6 $155.92   3.531%   $161.4255   $161.43   $161.45   $161.40  
  Purchase #7 $129.32   4.690%   $135.3851   $135.39   $135.40   $135.40  
  7 purchase totals = $1,142.52       $1,232.2399   $1,232.25   $1,232.30   $1,232.20