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 $249.32   8.121%   $269.5673   $269.57   $269.55   $269.60  
  Purchase #2 $206.60   7.611%   $222.3243   $222.32   $222.30   $222.30  
  Purchase #3 $234.49   5.656%   $247.7528   $247.75   $247.75   $247.80  
  Purchase #4 $205.73   9.405%   $225.0789   $225.08   $225.10   $225.10  
  Purchase #5 $177.37   3.786%   $184.0852   $184.09   $184.10   $184.10  
  Purchase #6 $152.75   7.789%   $164.6477   $164.65   $164.65   $164.60  
  Purchase #7 $215.95   7.219%   $231.5394   $231.54   $231.55   $231.50  
  7 purchase totals = $1,442.21       $1,544.9956   $1,545.00   $1,545.00   $1,545.00