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 $76.87   13.129%   $86.9623   $86.96   $86.95   $87.00  
  Purchase #2 $246.53   6.557%   $262.695   $262.70   $262.70   $262.70  
  Purchase #3 $65.64   12.780%   $74.0288   $74.03   $74.05   $74.00  
  Purchase #4 $101.88   7.576%   $109.5984   $109.60   $109.60   $109.60  
  Purchase #5 $35.95   5.828%   $38.0452   $38.05   $38.05   $38.00  
  Purchase #6 $52.81   12.815%   $59.5776   $59.58   $59.60   $59.60  
  Purchase #7 $30.43   6.267%   $32.337   $32.34   $32.35   $32.30  
  7 purchase totals = $610.11       $663.2443   $663.26   $663.30   $663.20