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 $88.78   3.110%   $91.5411   $91.54   $91.55   $91.50  
  Purchase #2 $48.43   9.646%   $53.1016   $53.10   $53.10   $53.10  
  Purchase #3 $53.85   13.517%   $61.1289   $61.13   $61.15   $61.10  
  Purchase #4 $231.26   13.535%   $262.561   $262.56   $262.55   $262.60  
  Purchase #5 $232.51   3.676%   $241.0571   $241.06   $241.05   $241.10  
  Purchase #6 $184.51   12.410%   $207.4077   $207.41   $207.40   $207.40  
  Purchase #7 $153.85   5.106%   $161.7056   $161.71   $161.70   $161.70  
  7 purchase totals = $993.19       $1,078.5030   $1,078.51   $1,078.50   $1,078.50