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 $93.56   12.591%   $105.3401   $105.34   $105.35   $105.30  
  Purchase #2 $202.35   11.125%   $224.8614   $224.86   $224.85   $224.90  
  Purchase #3 $166.30   12.182%   $186.5587   $186.56   $186.55   $186.60  
  Purchase #4 $233.65   7.623%   $251.4611   $251.46   $251.45   $251.50  
  Purchase #5 $52.83   4.766%   $55.3479   $55.35   $55.35   $55.30  
  Purchase #6 $231.52   8.157%   $250.4051   $250.41   $250.40   $250.40  
  Purchase #7 $85.88   13.829%   $97.7563   $97.76   $97.75   $97.80  
  7 purchase totals = $1,066.09       $1,171.7306   $1,171.74   $1,171.70   $1,171.80