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 $14.79   11.779%   $16.5321   $16.53   $16.55   $16.50  
  Purchase #2 $176.31   6.555%   $187.8671   $187.87   $187.85   $187.90  
  Purchase #3 $116.81   3.271%   $120.6309   $120.63   $120.65   $120.60  
  Purchase #4 $229.31   9.671%   $251.4866   $251.49   $251.50   $251.50  
  Purchase #5 $212.58   13.459%   $241.1911   $241.19   $241.20   $241.20  
  Purchase #6 $208.52   7.166%   $223.4625   $223.46   $223.45   $223.50  
  Purchase #7 $117.85   9.427%   $128.9597   $128.96   $128.95   $129.00  
  7 purchase totals = $1,076.17       $1,170.1300   $1,170.13   $1,170.15   $1,170.20