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 $153.37   6.340%   $163.0937   $163.09   $163.10   $163.10  
  Purchase #2 $162.95   5.405%   $171.7574   $171.76   $171.75   $171.80  
  Purchase #3 $71.84   6.779%   $76.71   $76.71   $76.70   $76.70  
  Purchase #4 $33.61   7.553%   $36.1486   $36.15   $36.15   $36.10  
  Purchase #5 $169.53   5.848%   $179.4441   $179.44   $179.45   $179.40  
  Purchase #6 $219.55   10.118%   $241.7641   $241.76   $241.75   $241.80  
  Purchase #7 $170.77   10.852%   $189.302   $189.30   $189.30   $189.30  
  7 purchase totals = $981.62       $1,058.2199   $1,058.21   $1,058.20   $1,058.20