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 $185.46   4.612%   $194.0134   $194.01   $194.00   $194.00  
  Purchase #2 $166.37   8.544%   $180.5847   $180.58   $180.60   $180.60  
  Purchase #3 $247.49   3.654%   $256.5333   $256.53   $256.55   $256.50  
  Purchase #4 $143.65   13.432%   $162.9451   $162.95   $162.95   $162.90  
  Purchase #5 $133.68   13.682%   $151.9701   $151.97   $151.95   $152.00  
  Purchase #6 $25.81   4.482%   $26.9668   $26.97   $26.95   $27.00  
  Purchase #7 $216.72   11.503%   $241.6493   $241.65   $241.65   $241.60  
  7 purchase totals = $1,119.18       $1,214.6627   $1,214.66   $1,214.65   $1,214.60