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 $36.81   4.442%   $38.4451   $38.45   $38.45   $38.40  
  Purchase #2 $60.30   9.486%   $66.0201   $66.02   $66.00   $66.00  
  Purchase #3 $181.36   12.424%   $203.8922   $203.89   $203.90   $203.90  
  Purchase #4 $84.67   13.667%   $96.2418   $96.24   $96.25   $96.20  
  Purchase #5 $123.75   4.337%   $129.117   $129.12   $129.10   $129.10  
  Purchase #6 $156.77   6.316%   $166.6716   $166.67   $166.65   $166.70  
  Purchase #7 $67.64   8.195%   $73.1831   $73.18   $73.20   $73.20  
  7 purchase totals = $711.30       $773.5709   $773.57   $773.55   $773.50