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 $169.60   5.272%   $178.5413   $178.54   $178.55   $178.50  
  Purchase #2 $164.39   11.844%   $183.8604   $183.86   $183.85   $183.90  
  Purchase #3 $59.42   12.653%   $66.9384   $66.94   $66.95   $66.90  
  Purchase #4 $48.58   9.423%   $53.1577   $53.16   $53.15   $53.20  
  Purchase #5 $175.48   9.345%   $191.8786   $191.88   $191.90   $191.90  
  Purchase #6 $146.80   4.273%   $153.0728   $153.07   $153.05   $153.10  
  Purchase #7 $169.67   10.207%   $186.9882   $186.99   $187.00   $187.00  
  7 purchase totals = $933.94       $1,014.4374   $1,014.44   $1,014.45   $1,014.50