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 $126.94   11.500%   $141.5381   $141.54   $141.55   $141.50  
  Purchase #2 $136.37   13.446%   $154.7063   $154.71   $154.70   $154.70  
  Purchase #3 $182.98   3.337%   $189.086   $189.09   $189.10   $189.10  
  Purchase #4 $167.48   6.722%   $178.738   $178.74   $178.75   $178.70  
  Purchase #5 $26.49   9.806%   $29.0876   $29.09   $29.10   $29.10  
  Purchase #6 $243.67   8.162%   $263.5583   $263.56   $263.55   $263.60  
  Purchase #7 $67.31   4.405%   $70.275   $70.28   $70.30   $70.30  
  7 purchase totals = $951.24       $1,026.9893   $1,027.01   $1,027.05   $1,027.00