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 $168.84   13.756%   $192.0656   $192.07   $192.05   $192.10  
  Purchase #2 $26.84   5.194%   $28.2341   $28.23   $28.25   $28.20  
  Purchase #3 $194.60   9.824%   $213.7175   $213.72   $213.70   $213.70  
  Purchase #4 $100.63   6.352%   $107.022   $107.02   $107.00   $107.00  
  Purchase #5 $194.63   9.150%   $212.4386   $212.44   $212.45   $212.40  
  Purchase #6 $51.67   6.631%   $55.0962   $55.10   $55.10   $55.10  
  Purchase #7 $173.85   13.726%   $197.7127   $197.71   $197.70   $197.70  
  7 purchase totals = $911.06       $1,006.2867   $1,006.29   $1,006.25   $1,006.20