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 $183.53   5.588%   $193.7857   $193.79   $193.80   $193.80  
  Purchase #2 $50.97   7.126%   $54.6021   $54.60   $54.60   $54.60  
  Purchase #3 $233.45   9.513%   $255.6581   $255.66   $255.65   $255.70  
  Purchase #4 $248.35   5.557%   $262.1508   $262.15   $262.15   $262.20  
  Purchase #5 $122.62   6.227%   $130.2555   $130.26   $130.25   $130.30  
  Purchase #6 $188.68   11.461%   $210.3046   $210.30   $210.30   $210.30  
  Purchase #7 $62.68   3.553%   $64.907   $64.91   $64.90   $64.90  
  7 purchase totals = $1,090.28       $1,171.6638   $1,171.67   $1,171.65   $1,171.80