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 $210.58   12.683%   $237.2879   $237.29   $237.30   $237.30  
  Purchase #2 $212.28   12.287%   $238.3628   $238.36   $238.35   $238.40  
  Purchase #3 $147.32   5.111%   $154.8495   $154.85   $154.85   $154.80  
  Purchase #4 $231.52   3.403%   $239.3986   $239.40   $239.40   $239.40  
  Purchase #5 $32.86   9.157%   $35.869   $35.87   $35.85   $35.90  
  Purchase #6 $134.79   7.425%   $144.7982   $144.80   $144.80   $144.80  
  Purchase #7 $24.78   6.777%   $26.4593   $26.46   $26.45   $26.50  
  7 purchase totals = $994.13       $1,077.0253   $1,077.03   $1,077.00   $1,077.10