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 $44.35   6.615%   $47.2838   $47.28   $47.30   $47.30  
  Purchase #2 $192.65   10.652%   $213.1711   $213.17   $213.15   $213.20  
  Purchase #3 $53.33   5.530%   $56.2791   $56.28   $56.30   $56.30  
  Purchase #4 $179.27   7.341%   $192.4302   $192.43   $192.45   $192.40  
  Purchase #5 $129.45   5.364%   $136.3937   $136.39   $136.40   $136.40  
  Purchase #6 $137.53   9.809%   $151.0203   $151.02   $151.00   $151.00  
  Purchase #7 $10.29   6.254%   $10.9335   $10.93   $10.95   $10.90  
  7 purchase totals = $746.87       $807.5117   $807.50   $807.55   $807.50