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 $219.80   12.645%   $247.5937   $247.59   $247.60   $247.60  
  Purchase #2 $248.84   12.517%   $279.9873   $279.99   $280.00   $280.00  
  Purchase #3 $61.52   9.774%   $67.533   $67.53   $67.55   $67.50  
  Purchase #4 $44.46   5.555%   $46.9298   $46.93   $46.95   $46.90  
  Purchase #5 $22.77   5.521%   $24.0271   $24.03   $24.05   $24.00  
  Purchase #6 $247.73   13.760%   $281.8176   $281.82   $281.80   $281.80  
  Purchase #7 $197.40   7.246%   $211.7036   $211.70   $211.70   $211.70  
  7 purchase totals = $1,042.52       $1,159.5921   $1,159.59   $1,159.65   $1,159.50