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 $200.55   12.746%   $226.1121   $226.11   $226.10   $226.10  
  Purchase #2 $146.52   6.693%   $156.3266   $156.33   $156.35   $156.30  
  Purchase #3 $234.89   11.607%   $262.1537   $262.15   $262.15   $262.20  
  Purchase #4 $63.44   10.145%   $69.876   $69.88   $69.90   $69.90  
  Purchase #5 $161.88   6.293%   $172.0671   $172.07   $172.05   $172.10  
  Purchase #6 $31.64   10.643%   $35.0074   $35.01   $35.00   $35.00  
  Purchase #7 $134.67   3.301%   $139.1155   $139.12   $139.10   $139.10  
  7 purchase totals = $973.59       $1,060.6584   $1,060.67   $1,060.65   $1,060.70