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 $88.92   5.785%   $94.064   $94.06   $94.05   $94.10  
  Purchase #2 $73.53   10.501%   $81.2514   $81.25   $81.25   $81.30  
  Purchase #3 $9.70   5.346%   $10.2186   $10.22   $10.20   $10.20  
  Purchase #4 $54.68   6.759%   $58.3758   $58.38   $58.40   $58.40  
  Purchase #5 $223.48   7.533%   $240.3147   $240.31   $240.30   $240.30  
  Purchase #6 $219.32   5.311%   $230.9681   $230.97   $230.95   $231.00  
  Purchase #7 $221.39   12.401%   $248.8446   $248.84   $248.85   $248.80  
  7 purchase totals = $891.02       $964.0372   $964.03   $964.00   $964.10