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 $61.42   7.212%   $65.8496   $65.85   $65.85   $65.80  
  Purchase #2 $163.48   6.637%   $174.3302   $174.33   $174.35   $174.30  
  Purchase #3 $89.32   4.643%   $93.4671   $93.47   $93.45   $93.50  
  Purchase #4 $220.58   7.822%   $237.8338   $237.83   $237.85   $237.80  
  Purchase #5 $63.79   3.619%   $66.0986   $66.10   $66.10   $66.10  
  Purchase #6 $130.82   9.458%   $143.193   $143.19   $143.20   $143.20  
  Purchase #7 $229.75   13.350%   $260.4216   $260.42   $260.40   $260.40  
  7 purchase totals = $959.16       $1,041.1939   $1,041.19   $1,041.20   $1,041.10