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 $202.63   10.669%   $224.2486   $224.25   $224.25   $224.20  
  Purchase #2 $135.72   13.691%   $154.3014   $154.30   $154.30   $154.30  
  Purchase #3 $28.51   10.109%   $31.3921   $31.39   $31.40   $31.40  
  Purchase #4 $93.32   4.205%   $97.2441   $97.24   $97.25   $97.20  
  Purchase #5 $103.32   5.816%   $109.3291   $109.33   $109.35   $109.30  
  Purchase #6 $67.87   10.803%   $75.202   $75.20   $75.20   $75.20  
  Purchase #7 $177.25   13.871%   $201.8363   $201.84   $201.85   $201.80  
  7 purchase totals = $808.62       $893.5536   $893.55   $893.60   $893.40