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 $244.69   8.779%   $266.1713   $266.17   $266.15   $266.20  
  Purchase #2 $138.67   3.554%   $143.5983   $143.60   $143.60   $143.60  
  Purchase #3 $220.82   9.625%   $242.0739   $242.07   $242.05   $242.10  
  Purchase #4 $141.58   10.779%   $156.8409   $156.84   $156.85   $156.80  
  Purchase #5 $34.32   5.354%   $36.1575   $36.16   $36.15   $36.20  
  Purchase #6 $180.62   10.219%   $199.0776   $199.08   $199.10   $199.10  
  Purchase #7 $10.80   11.349%   $12.0257   $12.03   $12.05   $12.00  
  7 purchase totals = $971.50       $1,055.9452   $1,055.95   $1,055.95   $1,056.00