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 $156.27   12.643%   $176.0272   $176.03   $176.05   $176.00  
  Purchase #2 $64.91   11.770%   $72.5499   $72.55   $72.55   $72.50  
  Purchase #3 $87.50   8.531%   $94.9646   $94.96   $94.95   $95.00  
  Purchase #4 $53.40   4.701%   $55.9103   $55.91   $55.90   $55.90  
  Purchase #5 $80.81   7.170%   $86.6041   $86.60   $86.60   $86.60  
  Purchase #6 $221.42   11.482%   $246.8434   $246.84   $246.85   $246.80  
  Purchase #7 $16.57   9.137%   $18.084   $18.08   $18.10   $18.10  
  7 purchase totals = $680.88       $750.9835   $750.97   $751.00   $750.90