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 $158.36   11.225%   $176.1359   $176.14   $176.15   $176.10  
  Purchase #2 $52.85   7.265%   $56.6896   $56.69   $56.70   $56.70  
  Purchase #3 $23.97   11.751%   $26.7867   $26.79   $26.80   $26.80  
  Purchase #4 $34.59   12.818%   $39.0237   $39.02   $39.00   $39.00  
  Purchase #5 $161.35   13.654%   $183.3807   $183.38   $183.40   $183.40  
  Purchase #6 $128.36   5.236%   $135.0809   $135.08   $135.10   $135.10  
  Purchase #7 $118.99   9.344%   $130.1084   $130.11   $130.10   $130.10  
  7 purchase totals = $678.47       $747.2059   $747.21   $747.25   $747.20