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 $84.87   4.246%   $88.4736   $88.47   $88.45   $88.50  
  Purchase #2 $55.51   4.317%   $57.9064   $57.91   $57.90   $57.90  
  Purchase #3 $211.82   11.208%   $235.5608   $235.56   $235.55   $235.60  
  Purchase #4 $165.25   12.641%   $186.1393   $186.14   $186.15   $186.10  
  Purchase #5 $68.78   8.780%   $74.8189   $74.82   $74.80   $74.80  
  Purchase #6 $250.55   12.597%   $282.1118   $282.11   $282.10   $282.10  
  Purchase #7 $80.95   11.841%   $90.5353   $90.54   $90.55   $90.50  
  7 purchase totals = $917.73       $1,015.5461   $1,015.55   $1,015.50   $1,015.50