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 $222.29   8.765%   $241.7737   $241.77   $241.75   $241.80  
  Purchase #2 $40.68   9.726%   $44.6365   $44.64   $44.65   $44.60  
  Purchase #3 $177.70   13.130%   $201.032   $201.03   $201.05   $201.00  
  Purchase #4 $176.57   6.247%   $187.6003   $187.60   $187.60   $187.60  
  Purchase #5 $91.33   12.120%   $102.3992   $102.40   $102.40   $102.40  
  Purchase #6 $155.72   5.736%   $164.6521   $164.65   $164.65   $164.70  
  Purchase #7 $56.99   6.536%   $60.7149   $60.71   $60.70   $60.70  
  7 purchase totals = $921.28       $1,002.8087   $1,002.80   $1,002.80   $1,002.80