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 $83.46   12.847%   $94.1821   $94.18   $94.20   $94.20  
  Purchase #2 $105.82   4.237%   $110.3036   $110.30   $110.30   $110.30  
  Purchase #3 $124.27   11.517%   $138.5822   $138.58   $138.60   $138.60  
  Purchase #4 $248.99   3.718%   $258.2474   $258.25   $258.25   $258.20  
  Purchase #5 $223.72   5.328%   $235.6398   $235.64   $235.65   $235.60  
  Purchase #6 $198.69   8.154%   $214.8912   $214.89   $214.90   $214.90  
  Purchase #7 $207.86   5.655%   $219.6145   $219.61   $219.60   $219.60  
  7 purchase totals = $1,192.81       $1,271.4608   $1,271.45   $1,271.50   $1,271.40