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 $191.90   6.829%   $205.0049   $205.00   $205.00   $205.00  
  Purchase #2 $142.97   6.833%   $152.7391   $152.74   $152.75   $152.70  
  Purchase #3 $65.50   5.360%   $69.0108   $69.01   $69.00   $69.00  
  Purchase #4 $214.36   6.720%   $228.765   $228.77   $228.75   $228.80  
  Purchase #5 $184.53   12.311%   $207.2475   $207.25   $207.25   $207.20  
  Purchase #6 $202.64   9.479%   $221.8482   $221.85   $221.85   $221.80  
  Purchase #7 $33.84   4.237%   $35.2738   $35.27   $35.25   $35.30  
  7 purchase totals = $1,035.74       $1,119.8893   $1,119.89   $1,119.85   $1,119.80