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 $56.95   7.743%   $61.3596   $61.36   $61.35   $61.40  
  Purchase #2 $104.90   3.479%   $108.5495   $108.55   $108.55   $108.50  
  Purchase #3 $200.43   10.264%   $221.0021   $221.00   $221.00   $221.00  
  Purchase #4 $176.27   6.630%   $187.9567   $187.96   $187.95   $188.00  
  Purchase #5 $165.80   6.176%   $176.0398   $176.04   $176.05   $176.00  
  Purchase #6 $124.25   8.419%   $134.7106   $134.71   $134.70   $134.70  
  Purchase #7 $32.65   9.611%   $35.788   $35.79   $35.80   $35.80  
  7 purchase totals = $861.25       $925.4063   $925.41   $925.40   $925.40