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 $32.67   8.751%   $35.529   $35.53   $35.55   $35.50  
  Purchase #2 $225.80   10.377%   $249.2313   $249.23   $249.25   $249.20  
  Purchase #3 $91.44   6.627%   $97.4997   $97.50   $97.50   $97.50  
  Purchase #4 $231.99   8.809%   $252.426   $252.43   $252.45   $252.40  
  Purchase #5 $204.60   8.630%   $222.257   $222.26   $222.25   $222.30  
  Purchase #6 $156.45   5.731%   $165.4161   $165.42   $165.40   $165.40  
  Purchase #7 $234.92   8.195%   $254.1717   $254.17   $254.15   $254.20  
  7 purchase totals = $1,177.87       $1,276.5308   $1,276.54   $1,276.55   $1,276.50