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 $96.85   4.739%   $101.4397   $101.44   $101.45   $101.40  
  Purchase #2 $32.39   4.336%   $33.7944   $33.79   $33.80   $33.80  
  Purchase #3 $202.97   11.681%   $226.6789   $226.68   $226.70   $226.70  
  Purchase #4 $181.28   5.188%   $190.6848   $190.68   $190.70   $190.70  
  Purchase #5 $90.94   6.280%   $96.651   $96.65   $96.65   $96.70  
  Purchase #6 $108.66   7.834%   $117.1724   $117.17   $117.15   $117.20  
  Purchase #7 $153.75   3.432%   $159.0267   $159.03   $159.05   $159.00  
  7 purchase totals = $866.84       $925.4479   $925.44   $925.50   $925.50