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 $153.99   13.323%   $174.5061   $174.51   $174.50   $174.50  
  Purchase #2 $44.63   9.114%   $48.6976   $48.70   $48.70   $48.70  
  Purchase #3 $123.80   6.386%   $131.7059   $131.71   $131.70   $131.70  
  Purchase #4 $173.32   13.202%   $196.2017   $196.20   $196.20   $196.20  
  Purchase #5 $201.71   5.394%   $212.5902   $212.59   $212.60   $212.60  
  Purchase #6 $130.55   6.421%   $138.9326   $138.93   $138.95   $138.90  
  Purchase #7 $248.42   3.131%   $256.198   $256.20   $256.20   $256.20  
  7 purchase totals = $1,076.42       $1,158.8321   $1,158.84   $1,158.85   $1,158.80