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 $58.95   8.759%   $64.1134   $64.11   $64.10   $64.10  
  Purchase #2 $75.75   5.281%   $79.7504   $79.75   $79.75   $79.80  
  Purchase #3 $201.69   9.570%   $220.9917   $220.99   $221.00   $221.00  
  Purchase #4 $68.62   5.529%   $72.414   $72.41   $72.40   $72.40  
  Purchase #5 $198.27   8.275%   $214.6768   $214.68   $214.70   $214.70  
  Purchase #6 $150.40   13.785%   $171.1326   $171.13   $171.15   $171.10  
  Purchase #7 $179.88   6.275%   $191.1675   $191.17   $191.15   $191.20  
  7 purchase totals = $933.56       $1,014.2464   $1,014.24   $1,014.25   $1,014.30