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 $102.85   4.619%   $107.6006   $107.60   $107.60   $107.60  
  Purchase #2 $189.37   11.438%   $211.0301   $211.03   $211.05   $211.00  
  Purchase #3 $24.87   9.134%   $27.1416   $27.14   $27.15   $27.10  
  Purchase #4 $177.78   13.374%   $201.5563   $201.56   $201.55   $201.60  
  Purchase #5 $69.72   11.196%   $77.5259   $77.53   $77.55   $77.50  
  Purchase #6 $226.67   6.666%   $241.7798   $241.78   $241.80   $241.80  
  Purchase #7 $151.91   6.601%   $161.9376   $161.94   $161.95   $161.90  
  7 purchase totals = $943.17       $1,028.5719   $1,028.58   $1,028.65   $1,028.50