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 $58.51   8.217%   $63.3178   $63.32   $63.30   $63.30  
  Purchase #2 $164.90   12.460%   $185.4465   $185.45   $185.45   $185.40  
  Purchase #3 $250.74   3.747%   $260.1352   $260.14   $260.15   $260.10  
  Purchase #4 $179.85   11.765%   $201.0094   $201.01   $201.00   $201.00  
  Purchase #5 $188.56   13.248%   $213.5404   $213.54   $213.55   $213.50  
  Purchase #6 $68.87   11.810%   $77.0035   $77.00   $77.00   $77.00  
  Purchase #7 $206.76   6.212%   $219.6039   $219.60   $219.60   $219.60  
  7 purchase totals = $1,118.19       $1,220.0567   $1,220.06   $1,220.05   $1,219.90