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 $87.64   11.413%   $97.6424   $97.64   $97.65   $97.60  
  Purchase #2 $230.92   13.178%   $261.3506   $261.35   $261.35   $261.40  
  Purchase #3 $249.77   10.375%   $275.6836   $275.68   $275.70   $275.70  
  Purchase #4 $171.84   10.627%   $190.1014   $190.10   $190.10   $190.10  
  Purchase #5 $35.72   6.316%   $37.9761   $37.98   $38.00   $38.00  
  Purchase #6 $180.54   6.786%   $192.7914   $192.79   $192.80   $192.80  
  Purchase #7 $194.61   11.153%   $216.3149   $216.31   $216.30   $216.30  
  7 purchase totals = $1,151.04       $1,271.8604   $1,271.85   $1,271.90   $1,271.90