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 $208.39   12.821%   $235.1077   $235.11   $235.10   $235.10  
  Purchase #2 $243.50   9.599%   $266.8736   $266.87   $266.85   $266.90  
  Purchase #3 $98.37   13.866%   $112.01   $112.01   $112.00   $112.00  
  Purchase #4 $35.58   5.612%   $37.5767   $37.58   $37.60   $37.60  
  Purchase #5 $62.31   5.404%   $65.6772   $65.68   $65.70   $65.70  
  Purchase #6 $52.97   6.320%   $56.3177   $56.32   $56.30   $56.30  
  Purchase #7 $22.86   9.364%   $25.0006   $25.00   $25.00   $25.00  
  7 purchase totals = $723.98       $798.5635   $798.57   $798.55   $798.60