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 $89.96   6.136%   $95.4799   $95.48   $95.50   $95.50  
  Purchase #2 $155.96   13.349%   $176.7791   $176.78   $176.80   $176.80  
  Purchase #3 $189.91   9.286%   $207.545   $207.55   $207.55   $207.50  
  Purchase #4 $158.51   5.516%   $167.2534   $167.25   $167.25   $167.30  
  Purchase #5 $219.61   4.867%   $230.2984   $230.30   $230.30   $230.30  
  Purchase #6 $184.74   4.248%   $192.5878   $192.59   $192.60   $192.60  
  Purchase #7 $158.45   6.498%   $168.7461   $168.75   $168.75   $168.70  
  7 purchase totals = $1,157.14       $1,238.6897   $1,238.70   $1,238.75   $1,238.70