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 $141.98   9.629%   $155.6513   $155.65   $155.65   $155.70  
  Purchase #2 $249.67   4.181%   $260.1087   $260.11   $260.10   $260.10  
  Purchase #3 $56.44   8.479%   $61.2255   $61.23   $61.25   $61.20  
  Purchase #4 $23.33   6.285%   $24.7963   $24.80   $24.80   $24.80  
  Purchase #5 $176.69   7.458%   $189.8675   $189.87   $189.85   $189.90  
  Purchase #6 $221.62   7.608%   $238.4808   $238.48   $238.50   $238.50  
  Purchase #7 $121.32   8.286%   $131.3726   $131.37   $131.35   $131.40  
  7 purchase totals = $991.05       $1,061.5027   $1,061.51   $1,061.50   $1,061.60