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 $56.41   11.741%   $63.0331   $63.03   $63.05   $63.00  
  Purchase #2 $48.81   8.157%   $52.7914   $52.79   $52.80   $52.80  
  Purchase #3 $188.58   7.230%   $202.2143   $202.21   $202.20   $202.20  
  Purchase #4 $114.91   6.326%   $122.1792   $122.18   $122.20   $122.20  
  Purchase #5 $74.60   3.215%   $76.9984   $77.00   $77.00   $77.00  
  Purchase #6 $111.46   8.172%   $120.5685   $120.57   $120.55   $120.60  
  Purchase #7 $174.40   7.693%   $187.8166   $187.82   $187.80   $187.80  
  7 purchase totals = $769.17       $825.6015   $825.60   $825.60   $825.60