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 $210.48   11.435%   $234.5484   $234.55   $234.55   $234.50  
  Purchase #2 $60.52   13.424%   $68.6442   $68.64   $68.65   $68.60  
  Purchase #3 $103.67   7.779%   $111.7345   $111.73   $111.75   $111.70  
  Purchase #4 $35.41   3.783%   $36.7496   $36.75   $36.75   $36.70  
  Purchase #5 $215.31   11.140%   $239.2955   $239.30   $239.30   $239.30  
  Purchase #6 $195.56   5.337%   $205.997   $206.00   $206.00   $206.00  
  Purchase #7 $250.41   13.685%   $284.6786   $284.68   $284.70   $284.70  
  7 purchase totals = $1,071.36       $1,181.6478   $1,181.65   $1,181.70   $1,181.50