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 $162.95   7.441%   $175.0751   $175.08   $175.10   $175.10  
  Purchase #2 $97.68   6.320%   $103.8534   $103.85   $103.85   $103.90  
  Purchase #3 $52.57   9.556%   $57.5936   $57.59   $57.60   $57.60  
  Purchase #4 $174.55   5.552%   $184.241   $184.24   $184.25   $184.20  
  Purchase #5 $78.70   11.707%   $87.9134   $87.91   $87.90   $87.90  
  Purchase #6 $222.64   10.706%   $246.4758   $246.48   $246.50   $246.50  
  Purchase #7 $12.75   7.262%   $13.6759   $13.68   $13.70   $13.70  
  7 purchase totals = $801.84       $868.8282   $868.83   $868.90   $868.90