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 $162.47   11.707%   $181.4904   $181.49   $181.50   $181.50  
  Purchase #2 $62.95   5.570%   $66.4563   $66.46   $66.45   $66.50  
  Purchase #3 $246.57   7.232%   $264.4019   $264.40   $264.40   $264.40  
  Purchase #4 $193.94   8.242%   $209.9245   $209.92   $209.90   $209.90  
  Purchase #5 $59.37   9.637%   $65.0915   $65.09   $65.10   $65.10  
  Purchase #6 $6.51   4.593%   $6.809   $6.81   $6.80   $6.80  
  Purchase #7 $67.51   8.411%   $73.1883   $73.19   $73.20   $73.20  
  7 purchase totals = $799.32       $867.3619   $867.36   $867.35   $867.40