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 $85.99   8.438%   $93.2458   $93.25   $93.25   $93.20  
  Purchase #2 $248.86   7.643%   $267.8804   $267.88   $267.90   $267.90  
  Purchase #3 $230.64   5.495%   $243.3137   $243.31   $243.30   $243.30  
  Purchase #4 $57.94   4.850%   $60.7501   $60.75   $60.75   $60.80  
  Purchase #5 $151.76   4.765%   $158.9914   $158.99   $159.00   $159.00  
  Purchase #6 $36.56   6.502%   $38.9371   $38.94   $38.95   $38.90  
  Purchase #7 $165.56   9.532%   $181.3412   $181.34   $181.35   $181.30  
  7 purchase totals = $977.31       $1,044.4597   $1,044.46   $1,044.50   $1,044.40