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 $243.96   9.651%   $267.5046   $267.50   $267.50   $267.50  
  Purchase #2 $64.72   3.872%   $67.226   $67.23   $67.25   $67.20  
  Purchase #3 $87.76   4.755%   $91.933   $91.93   $91.95   $91.90  
  Purchase #4 $96.56   4.108%   $100.5267   $100.53   $100.55   $100.50  
  Purchase #5 $48.35   8.772%   $52.5913   $52.59   $52.60   $52.60  
  Purchase #6 $193.93   6.508%   $206.551   $206.55   $206.55   $206.60  
  Purchase #7 $229.82   12.154%   $257.7523   $257.75   $257.75   $257.80  
  7 purchase totals = $965.10       $1,044.0849   $1,044.08   $1,044.15   $1,044.10