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 $104.26   5.394%   $109.8838   $109.88   $109.90   $109.90  
  Purchase #2 $25.35   10.658%   $28.0518   $28.05   $28.05   $28.10  
  Purchase #3 $172.44   7.210%   $184.8729   $184.87   $184.85   $184.90  
  Purchase #4 $158.40   5.240%   $166.7002   $166.70   $166.70   $166.70  
  Purchase #5 $145.78   8.371%   $157.9832   $157.98   $158.00   $158.00  
  Purchase #6 $18.37   7.656%   $19.7764   $19.78   $19.80   $19.80  
  Purchase #7 $15.25   9.351%   $16.676   $16.68   $16.70   $16.70  
  7 purchase totals = $639.85       $683.9443   $683.94   $684.00   $684.10