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 $120.34   11.775%   $134.51   $134.51   $134.50   $134.50  
  Purchase #2 $190.98   3.171%   $197.036   $197.04   $197.05   $197.00  
  Purchase #3 $195.62   11.638%   $218.3863   $218.39   $218.40   $218.40  
  Purchase #4 $60.26   10.471%   $66.5698   $66.57   $66.55   $66.60  
  Purchase #5 $150.49   8.596%   $163.4261   $163.43   $163.45   $163.40  
  Purchase #6 $173.27   10.328%   $191.1653   $191.17   $191.15   $191.20  
  Purchase #7 $34.87   11.361%   $38.8316   $38.83   $38.85   $38.80  
  7 purchase totals = $925.83       $1,009.9251   $1,009.94   $1,009.95   $1,009.90