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 $212.39   11.368%   $236.5345   $236.53   $236.55   $236.50  
  Purchase #2 $24.99   10.290%   $27.5615   $27.56   $27.55   $27.60  
  Purchase #3 $248.73   3.359%   $257.0848   $257.08   $257.10   $257.10  
  Purchase #4 $163.95   12.613%   $184.629   $184.63   $184.65   $184.60  
  Purchase #5 $147.59   11.109%   $163.9858   $163.99   $164.00   $164.00  
  Purchase #6 $49.96   9.451%   $54.6817   $54.68   $54.70   $54.70  
  Purchase #7 $103.47   3.355%   $106.9414   $106.94   $106.95   $106.90  
  7 purchase totals = $951.08       $1,031.4187   $1,031.41   $1,031.50   $1,031.40