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 $59.97   3.479%   $62.0564   $62.06   $62.05   $62.10  
  Purchase #2 $86.67   4.769%   $90.8033   $90.80   $90.80   $90.80  
  Purchase #3 $60.81   7.311%   $65.2558   $65.26   $65.25   $65.30  
  Purchase #4 $87.70   9.195%   $95.764   $95.76   $95.75   $95.80  
  Purchase #5 $220.96   5.178%   $232.4013   $232.40   $232.40   $232.40  
  Purchase #6 $120.67   12.861%   $136.1894   $136.19   $136.20   $136.20  
  Purchase #7 $224.41   7.428%   $241.0792   $241.08   $241.10   $241.10  
  7 purchase totals = $861.19       $923.5494   $923.55   $923.55   $923.70