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 $185.85   8.159%   $201.0135   $201.01   $201.00   $201.00  
  Purchase #2 $186.28   11.243%   $207.2235   $207.22   $207.20   $207.20  
  Purchase #3 $37.71   11.627%   $42.0945   $42.09   $42.10   $42.10  
  Purchase #4 $142.53   3.242%   $147.1508   $147.15   $147.15   $147.20  
  Purchase #5 $169.30   9.612%   $185.5731   $185.57   $185.55   $185.60  
  Purchase #6 $50.45   3.475%   $52.2031   $52.20   $52.20   $52.20  
  Purchase #7 $203.93   9.480%   $223.2626   $223.26   $223.25   $223.30  
  7 purchase totals = $976.05       $1,058.5211   $1,058.50   $1,058.45   $1,058.60