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 $87.25   12.837%   $98.4503   $98.45   $98.45   $98.50  
  Purchase #2 $62.87   11.824%   $70.3037   $70.30   $70.30   $70.30  
  Purchase #3 $204.76   9.185%   $223.5672   $223.57   $223.55   $223.60  
  Purchase #4 $22.46   9.833%   $24.6685   $24.67   $24.65   $24.70  
  Purchase #5 $182.41   8.229%   $197.4205   $197.42   $197.40   $197.40  
  Purchase #6 $169.37   4.354%   $176.7444   $176.74   $176.75   $176.70  
  Purchase #7 $222.81   6.836%   $238.0413   $238.04   $238.05   $238.00  
  7 purchase totals = $951.93       $1,029.1959   $1,029.19   $1,029.15   $1,029.20