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 $180.99   8.755%   $196.8357   $196.84   $196.85   $196.80  
  Purchase #2 $70.34   13.217%   $79.6368   $79.64   $79.65   $79.60  
  Purchase #3 $167.85   5.493%   $177.07   $177.07   $177.05   $177.10  
  Purchase #4 $110.37   13.584%   $125.3627   $125.36   $125.35   $125.40  
  Purchase #5 $65.66   5.616%   $69.3475   $69.35   $69.35   $69.30  
  Purchase #6 $227.96   12.387%   $256.1974   $256.20   $256.20   $256.20  
  Purchase #7 $117.39   9.527%   $128.5737   $128.57   $128.55   $128.60  
  7 purchase totals = $940.56       $1,033.0238   $1,033.03   $1,033.00   $1,033.00