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 $58.38   13.670%   $66.3605   $66.36   $66.35   $66.40  
  Purchase #2 $10.70   3.738%   $11.1   $11.10   $11.10   $11.10  
  Purchase #3 $218.51   10.225%   $240.8526   $240.85   $240.85   $240.90  
  Purchase #4 $194.48   4.118%   $202.4887   $202.49   $202.50   $202.50  
  Purchase #5 $190.94   6.720%   $203.7712   $203.77   $203.75   $203.80  
  Purchase #6 $227.36   7.348%   $244.0664   $244.07   $244.05   $244.10  
  Purchase #7 $134.89   5.390%   $142.1606   $142.16   $142.15   $142.20  
  7 purchase totals = $1,035.26       $1,110.8000   $1,110.80   $1,110.75   $1,111.00