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 $132.35   10.332%   $146.0244   $146.02   $146.00   $146.00  
  Purchase #2 $231.45   9.653%   $253.7919   $253.79   $253.80   $253.80  
  Purchase #3 $188.87   9.274%   $206.3858   $206.39   $206.40   $206.40  
  Purchase #4 $51.71   7.287%   $55.4781   $55.48   $55.50   $55.50  
  Purchase #5 $116.34   11.367%   $129.5644   $129.56   $129.55   $129.60  
  Purchase #6 $61.25   6.601%   $65.2931   $65.29   $65.30   $65.30  
  Purchase #7 $185.67   9.258%   $202.8593   $202.86   $202.85   $202.90  
  7 purchase totals = $967.64       $1,059.3970   $1,059.39   $1,059.40   $1,059.50