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 $60.91   7.581%   $65.5276   $65.53   $65.55   $65.50  
  Purchase #2 $56.48   8.197%   $61.1097   $61.11   $61.10   $61.10  
  Purchase #3 $68.82   12.814%   $77.6386   $77.64   $77.65   $77.60  
  Purchase #4 $67.66   10.827%   $74.9855   $74.99   $75.00   $75.00  
  Purchase #5 $160.94   11.702%   $179.7732   $179.77   $179.75   $179.80  
  Purchase #6 $130.87   6.386%   $139.2274   $139.23   $139.25   $139.20  
  Purchase #7 $131.79   8.614%   $143.1424   $143.14   $143.15   $143.10  
  7 purchase totals = $677.47       $741.4044   $741.41   $741.45   $741.30