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 $182.93   13.541%   $207.7006   $207.70   $207.70   $207.70  
  Purchase #2 $220.37   11.465%   $245.6354   $245.64   $245.65   $245.60  
  Purchase #3 $167.30   9.422%   $183.063   $183.06   $183.05   $183.10  
  Purchase #4 $186.51   9.841%   $204.8644   $204.86   $204.85   $204.90  
  Purchase #5 $43.38   13.251%   $49.1283   $49.13   $49.15   $49.10  
  Purchase #6 $147.46   10.699%   $163.2367   $163.24   $163.25   $163.20  
  Purchase #7 $192.29   12.140%   $215.634   $215.63   $215.65   $215.60  
  7 purchase totals = $1,140.24       $1,269.2624   $1,269.26   $1,269.30   $1,269.20