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 $93.30   3.153%   $96.2417   $96.24   $96.25   $96.20  
  Purchase #2 $70.32   4.284%   $73.3325   $73.33   $73.35   $73.30  
  Purchase #3 $161.96   9.529%   $177.3932   $177.39   $177.40   $177.40  
  Purchase #4 $173.42   8.489%   $188.1416   $188.14   $188.15   $188.10  
  Purchase #5 $11.49   7.258%   $12.3239   $12.32   $12.30   $12.30  
  Purchase #6 $27.62   12.427%   $31.0523   $31.05   $31.05   $31.10  
  Purchase #7 $243.97   9.219%   $266.4616   $266.46   $266.45   $266.50  
  7 purchase totals = $782.08       $844.9468   $844.93   $844.95   $844.90