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 $238.38   11.411%   $265.5815   $265.58   $265.60   $265.60  
  Purchase #2 $223.79   4.402%   $233.6412   $233.64   $233.65   $233.60  
  Purchase #3 $159.87   5.293%   $168.3319   $168.33   $168.35   $168.30  
  Purchase #4 $19.98   7.615%   $21.5015   $21.50   $21.50   $21.50  
  Purchase #5 $184.26   11.426%   $205.3135   $205.31   $205.30   $205.30  
  Purchase #6 $50.92   3.430%   $52.6666   $52.67   $52.65   $52.70  
  Purchase #7 $190.42   10.812%   $211.0082   $211.01   $211.00   $211.00  
  7 purchase totals = $1,067.62       $1,158.0444   $1,158.04   $1,158.05   $1,158.00