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 $119.27   6.114%   $126.5622   $126.56   $126.55   $126.60  
  Purchase #2 $181.54   6.512%   $193.3619   $193.36   $193.35   $193.40  
  Purchase #3 $63.91   8.851%   $69.5667   $69.57   $69.55   $69.60  
  Purchase #4 $47.54   6.795%   $50.7703   $50.77   $50.75   $50.80  
  Purchase #5 $93.92   13.356%   $106.464   $106.46   $106.45   $106.50  
  Purchase #6 $32.27   12.767%   $36.3899   $36.39   $36.40   $36.40  
  Purchase #7 $149.40   9.783%   $164.0158   $164.02   $164.00   $164.00  
  7 purchase totals = $687.85       $747.1308   $747.13   $747.05   $747.30