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 $60.68   13.339%   $68.7741   $68.77   $68.75   $68.80  
  Purchase #2 $180.28   12.155%   $202.193   $202.19   $202.20   $202.20  
  Purchase #3 $134.89   5.247%   $141.9677   $141.97   $141.95   $142.00  
  Purchase #4 $223.40   8.552%   $242.5052   $242.51   $242.50   $242.50  
  Purchase #5 $203.62   9.788%   $223.5503   $223.55   $223.55   $223.60  
  Purchase #6 $118.51   11.539%   $132.1849   $132.18   $132.20   $132.20  
  Purchase #7 $162.45   6.519%   $173.0401   $173.04   $173.05   $173.00  
  7 purchase totals = $1,083.83       $1,184.2153   $1,184.21   $1,184.20   $1,184.30