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 $184.60   10.829%   $204.5903   $204.59   $204.60   $204.60  
  Purchase #2 $14.45   13.194%   $16.3565   $16.36   $16.35   $16.40  
  Purchase #3 $222.51   12.815%   $251.0247   $251.02   $251.00   $251.00  
  Purchase #4 $176.68   6.190%   $187.6165   $187.62   $187.60   $187.60  
  Purchase #5 $40.62   4.528%   $42.4593   $42.46   $42.45   $42.50  
  Purchase #6 $95.88   13.598%   $108.9178   $108.92   $108.90   $108.90  
  Purchase #7 $202.65   6.325%   $215.4676   $215.47   $215.45   $215.50  
  7 purchase totals = $937.39       $1,026.4327   $1,026.44   $1,026.35   $1,026.50