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 $59.97   11.217%   $66.6968   $66.70   $66.70   $66.70  
  Purchase #2 $211.50   7.677%   $227.7369   $227.74   $227.75   $227.70  
  Purchase #3 $130.53   13.184%   $147.7391   $147.74   $147.75   $147.70  
  Purchase #4 $206.93   4.679%   $216.6123   $216.61   $216.60   $216.60  
  Purchase #5 $10.59   9.204%   $11.5647   $11.56   $11.55   $11.60  
  Purchase #6 $125.76   13.662%   $142.9413   $142.94   $142.95   $142.90  
  Purchase #7 $250.57   3.147%   $258.4554   $258.46   $258.45   $258.50  
  7 purchase totals = $995.85       $1,071.7465   $1,071.75   $1,071.75   $1,071.70