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 $63.82   8.215%   $69.0628   $69.06   $69.05   $69.10  
  Purchase #2 $166.60   10.763%   $184.5312   $184.53   $184.55   $184.50  
  Purchase #3 $104.99   11.416%   $116.9757   $116.98   $117.00   $117.00  
  Purchase #4 $143.52   13.229%   $162.5063   $162.51   $162.50   $162.50  
  Purchase #5 $225.26   8.783%   $245.0446   $245.04   $245.05   $245.00  
  Purchase #6 $189.95   10.716%   $210.305   $210.31   $210.30   $210.30  
  Purchase #7 $105.65   3.122%   $108.9484   $108.95   $108.95   $108.90  
  7 purchase totals = $999.79       $1,097.3740   $1,097.38   $1,097.40   $1,097.30