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 $165.98   12.793%   $187.2138   $187.21   $187.20   $187.20  
  Purchase #2 $171.83   13.693%   $195.3587   $195.36   $195.35   $195.40  
  Purchase #3 $224.40   12.299%   $251.999   $252.00   $252.00   $252.00  
  Purchase #4 $61.25   13.477%   $69.5047   $69.50   $69.50   $69.50  
  Purchase #5 $59.31   12.422%   $66.6775   $66.68   $66.70   $66.70  
  Purchase #6 $247.79   11.651%   $276.66   $276.66   $276.65   $276.70  
  Purchase #7 $190.96   11.171%   $212.2921   $212.29   $212.30   $212.30  
  7 purchase totals = $1,121.52       $1,259.7058   $1,259.70   $1,259.70   $1,259.80