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 $92.86   3.573%   $96.1779   $96.18   $96.20   $96.20  
  Purchase #2 $173.80   8.579%   $188.7103   $188.71   $188.70   $188.70  
  Purchase #3 $126.56   12.187%   $141.9839   $141.98   $142.00   $142.00  
  Purchase #4 $109.87   11.408%   $122.404   $122.40   $122.40   $122.40  
  Purchase #5 $167.36   4.126%   $174.2653   $174.27   $174.25   $174.30  
  Purchase #6 $190.46   4.793%   $199.5887   $199.59   $199.60   $199.60  
  Purchase #7 $70.42   9.624%   $77.1972   $77.20   $77.20   $77.20  
  7 purchase totals = $931.33       $1,000.3273   $1,000.33   $1,000.35   $1,000.40