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 $129.63   12.781%   $146.198   $146.20   $146.20   $146.20  
  Purchase #2 $202.69   9.294%   $221.528   $221.53   $221.55   $221.50  
  Purchase #3 $59.37   5.366%   $62.5558   $62.56   $62.55   $62.60  
  Purchase #4 $171.86   5.744%   $181.7316   $181.73   $181.75   $181.70  
  Purchase #5 $186.53   8.325%   $202.0586   $202.06   $202.05   $202.10  
  Purchase #6 $249.91   13.208%   $282.9181   $282.92   $282.90   $282.90  
  Purchase #7 $58.62   3.575%   $60.7157   $60.72   $60.70   $60.70  
  7 purchase totals = $1,058.61       $1,157.7058   $1,157.72   $1,157.70   $1,157.70