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 $48.50   7.769%   $52.268   $52.27   $52.25   $52.30  
  Purchase #2 $239.62   12.388%   $269.3041   $269.30   $269.30   $269.30  
  Purchase #3 $186.54   11.623%   $208.2215   $208.22   $208.20   $208.20  
  Purchase #4 $246.67   8.264%   $267.0548   $267.05   $267.05   $267.10  
  Purchase #5 $203.94   6.194%   $216.572   $216.57   $216.55   $216.60  
  Purchase #6 $79.57   11.166%   $88.4548   $88.45   $88.45   $88.50  
  Purchase #7 $149.50   5.740%   $158.0813   $158.08   $158.10   $158.10  
  7 purchase totals = $1,154.34       $1,259.9565   $1,259.94   $1,259.90   $1,260.10