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 $58.41   10.396%   $64.4823   $64.48   $64.50   $64.50  
  Purchase #2 $232.54   8.757%   $252.9035   $252.90   $252.90   $252.90  
  Purchase #3 $206.46   6.342%   $219.5537   $219.55   $219.55   $219.60  
  Purchase #4 $51.52   9.870%   $56.605   $56.61   $56.60   $56.60  
  Purchase #5 $174.28   9.687%   $191.1625   $191.16   $191.15   $191.20  
  Purchase #6 $77.42   9.792%   $85.001   $85.00   $85.00   $85.00  
  Purchase #7 $81.97   11.479%   $91.3793   $91.38   $91.40   $91.40  
  7 purchase totals = $882.60       $961.0873   $961.08   $961.10   $961.20