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 $147.80   12.654%   $166.5026   $166.50   $166.50   $166.50  
  Purchase #2 $235.97   11.440%   $262.965   $262.97   $262.95   $263.00  
  Purchase #3 $42.45   4.847%   $44.5076   $44.51   $44.50   $44.50  
  Purchase #4 $163.50   7.694%   $176.0797   $176.08   $176.10   $176.10  
  Purchase #5 $243.28   12.433%   $273.527   $273.53   $273.55   $273.50  
  Purchase #6 $14.71   10.138%   $16.2013   $16.20   $16.20   $16.20  
  Purchase #7 $198.58   13.607%   $225.6008   $225.60   $225.60   $225.60  
  7 purchase totals = $1,046.29       $1,165.3840   $1,165.39   $1,165.40   $1,165.40