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 $181.79   6.707%   $193.9827   $193.98   $194.00   $194.00  
  Purchase #2 $63.37   7.871%   $68.3579   $68.36   $68.35   $68.40  
  Purchase #3 $190.89   9.286%   $208.616   $208.62   $208.60   $208.60  
  Purchase #4 $73.37   4.367%   $76.5741   $76.57   $76.55   $76.60  
  Purchase #5 $246.59   12.459%   $277.3126   $277.31   $277.30   $277.30  
  Purchase #6 $58.57   5.294%   $61.6707   $61.67   $61.65   $61.70  
  Purchase #7 $115.90   9.602%   $127.0287   $127.03   $127.05   $127.00  
  7 purchase totals = $930.48       $1,013.5427   $1,013.54   $1,013.50   $1,013.60