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 $195.82   4.517%   $204.6652   $204.67   $204.65   $204.70  
  Purchase #2 $137.70   9.140%   $150.2858   $150.29   $150.30   $150.30  
  Purchase #3 $250.47   3.618%   $259.532   $259.53   $259.55   $259.50  
  Purchase #4 $52.80   11.267%   $58.749   $58.75   $58.75   $58.70  
  Purchase #5 $207.36   5.842%   $219.474   $219.47   $219.45   $219.50  
  Purchase #6 $81.74   5.368%   $86.1278   $86.13   $86.15   $86.10  
  Purchase #7 $187.65   9.188%   $204.8913   $204.89   $204.90   $204.90  
  7 purchase totals = $1,113.54       $1,183.7251   $1,183.73   $1,183.75   $1,183.70