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 $121.52   3.697%   $126.0126   $126.01   $126.00   $126.00  
  Purchase #2 $41.58   12.424%   $46.7459   $46.75   $46.75   $46.70  
  Purchase #3 $226.76   9.766%   $248.9054   $248.91   $248.90   $248.90  
  Purchase #4 $53.38   8.784%   $58.0689   $58.07   $58.05   $58.10  
  Purchase #5 $158.25   8.413%   $171.5636   $171.56   $171.55   $171.60  
  Purchase #6 $232.98   8.818%   $253.5242   $253.52   $253.50   $253.50  
  Purchase #7 $216.59   7.366%   $232.544   $232.54   $232.55   $232.50  
  7 purchase totals = $1,051.06       $1,137.3646   $1,137.36   $1,137.30   $1,137.30