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 $213.49   10.472%   $235.8467   $235.85   $235.85   $235.80  
  Purchase #2 $163.78   9.670%   $179.6175   $179.62   $179.60   $179.60  
  Purchase #3 $185.51   13.870%   $211.2402   $211.24   $211.25   $211.20  
  Purchase #4 $194.98   6.354%   $207.369   $207.37   $207.35   $207.40  
  Purchase #5 $186.87   9.198%   $204.0583   $204.06   $204.05   $204.10  
  Purchase #6 $190.38   11.801%   $212.8467   $212.85   $212.85   $212.80  
  Purchase #7 $86.32   8.227%   $93.4215   $93.42   $93.40   $93.40  
  7 purchase totals = $1,221.33       $1,344.3999   $1,344.41   $1,344.35   $1,344.30