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 $216.40   13.658%   $245.9559   $245.96   $245.95   $246.00  
  Purchase #2 $212.66   13.574%   $241.5265   $241.53   $241.55   $241.50  
  Purchase #3 $99.50   5.594%   $105.066   $105.07   $105.05   $105.10  
  Purchase #4 $44.28   9.184%   $48.3467   $48.35   $48.35   $48.30  
  Purchase #5 $194.58   13.557%   $220.9592   $220.96   $220.95   $221.00  
  Purchase #6 $91.51   8.221%   $99.033   $99.03   $99.05   $99.00  
  Purchase #7 $116.65   5.149%   $122.6563   $122.66   $122.65   $122.70  
  7 purchase totals = $975.58       $1,083.5436   $1,083.56   $1,083.55   $1,083.60