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 $118.82   9.691%   $130.3348   $130.33   $130.35   $130.30  
  Purchase #2 $149.89   11.177%   $166.6432   $166.64   $166.65   $166.60  
  Purchase #3 $205.80   5.541%   $217.2034   $217.20   $217.20   $217.20  
  Purchase #4 $126.99   9.390%   $138.9144   $138.91   $138.90   $138.90  
  Purchase #5 $73.27   5.647%   $77.4076   $77.41   $77.40   $77.40  
  Purchase #6 $193.40   9.207%   $211.2063   $211.21   $211.20   $211.20  
  Purchase #7 $74.85   7.873%   $80.7429   $80.74   $80.75   $80.70  
  7 purchase totals = $943.02       $1,022.4526   $1,022.44   $1,022.45   $1,022.30