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 $113.80   11.215%   $126.5627   $126.56   $126.55   $126.60  
  Purchase #2 $213.78   12.252%   $239.9723   $239.97   $239.95   $240.00  
  Purchase #3 $88.33   12.267%   $99.1654   $99.17   $99.15   $99.20  
  Purchase #4 $23.56   6.270%   $25.0372   $25.04   $25.05   $25.00  
  Purchase #5 $60.93   4.172%   $63.472   $63.47   $63.45   $63.50  
  Purchase #6 $172.81   11.112%   $192.0126   $192.01   $192.00   $192.00  
  Purchase #7 $21.44   4.496%   $22.4039   $22.40   $22.40   $22.40  
  7 purchase totals = $694.65       $768.6261   $768.62   $768.55   $768.70