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 $183.35   13.367%   $207.8584   $207.86   $207.85   $207.90  
  Purchase #2 $241.95   8.559%   $262.6585   $262.66   $262.65   $262.70  
  Purchase #3 $243.51   11.196%   $270.7734   $270.77   $270.75   $270.80  
  Purchase #4 $65.90   10.699%   $72.9506   $72.95   $72.95   $73.00  
  Purchase #5 $131.99   11.685%   $147.413   $147.41   $147.40   $147.40  
  Purchase #6 $93.59   3.790%   $97.1371   $97.14   $97.15   $97.10  
  Purchase #7 $111.94   10.203%   $123.3612   $123.36   $123.35   $123.40  
  7 purchase totals = $1,072.23       $1,182.1522   $1,182.15   $1,182.10   $1,182.30