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 $162.45   10.312%   $179.2018   $179.20   $179.20   $179.20  
  Purchase #2 $11.67   9.386%   $12.7653   $12.77   $12.75   $12.80  
  Purchase #3 $235.30   5.689%   $248.6862   $248.69   $248.70   $248.70  
  Purchase #4 $177.56   7.656%   $191.154   $191.15   $191.15   $191.20  
  Purchase #5 $178.48   5.570%   $188.4213   $188.42   $188.40   $188.40  
  Purchase #6 $200.67   5.618%   $211.9436   $211.94   $211.95   $211.90  
  Purchase #7 $33.65   8.847%   $36.627   $36.63   $36.65   $36.60  
  7 purchase totals = $999.78       $1,068.7992   $1,068.80   $1,068.80   $1,068.80