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 $92.50   11.784%   $103.4002   $103.40   $103.40   $103.40  
  Purchase #2 $24.46   10.635%   $27.0613   $27.06   $27.05   $27.10  
  Purchase #3 $245.26   9.705%   $269.0625   $269.06   $269.05   $269.10  
  Purchase #4 $87.33   5.376%   $92.0249   $92.02   $92.00   $92.00  
  Purchase #5 $222.50   6.186%   $236.2639   $236.26   $236.25   $236.30  
  Purchase #6 $168.32   9.817%   $184.844   $184.84   $184.85   $184.80  
  Purchase #7 $202.46   11.273%   $225.2833   $225.28   $225.30   $225.30  
  7 purchase totals = $1,042.83       $1,137.9401   $1,137.92   $1,137.90   $1,138.00