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 $58.95   9.258%   $64.4076   $64.41   $64.40   $64.40  
  Purchase #2 $156.66   3.623%   $162.3358   $162.34   $162.35   $162.30  
  Purchase #3 $232.95   9.481%   $255.036   $255.04   $255.05   $255.00  
  Purchase #4 $207.41   3.416%   $214.4951   $214.50   $214.50   $214.50  
  Purchase #5 $99.84   7.837%   $107.6645   $107.66   $107.65   $107.70  
  Purchase #6 $74.41   13.573%   $84.5097   $84.51   $84.50   $84.50  
  Purchase #7 $72.62   11.643%   $81.0751   $81.08   $81.10   $81.10  
  7 purchase totals = $902.84       $969.5238   $969.54   $969.55   $969.50