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 $88.77   8.666%   $96.4628   $96.46   $96.45   $96.50  
  Purchase #2 $110.61   12.690%   $124.6464   $124.65   $124.65   $124.60  
  Purchase #3 $228.30   9.301%   $249.5342   $249.53   $249.55   $249.50  
  Purchase #4 $156.87   6.335%   $166.8077   $166.81   $166.80   $166.80  
  Purchase #5 $180.55   12.371%   $202.8858   $202.89   $202.90   $202.90  
  Purchase #6 $114.36   13.560%   $129.8672   $129.87   $129.85   $129.90  
  Purchase #7 $37.74   4.868%   $39.5772   $39.58   $39.60   $39.60  
  7 purchase totals = $917.20       $1,009.7813   $1,009.79   $1,009.80   $1,009.80