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 $239.73   13.350%   $271.734   $271.73   $271.75   $271.70  
  Purchase #2 $90.55   6.580%   $96.5082   $96.51   $96.50   $96.50  
  Purchase #3 $73.65   10.599%   $81.4562   $81.46   $81.45   $81.50  
  Purchase #4 $10.81   8.471%   $11.7257   $11.73   $11.75   $11.70  
  Purchase #5 $176.27   3.221%   $181.9477   $181.95   $181.95   $181.90  
  Purchase #6 $143.57   4.797%   $150.4571   $150.46   $150.45   $150.50  
  Purchase #7 $244.47   6.460%   $260.2628   $260.26   $260.25   $260.30  
  7 purchase totals = $979.05       $1,054.0917   $1,054.10   $1,054.10   $1,054.10