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 $84.50   13.638%   $96.0241   $96.02   $96.00   $96.00  
  Purchase #2 $112.50   12.874%   $126.9833   $126.98   $127.00   $127.00  
  Purchase #3 $208.69   12.425%   $234.6197   $234.62   $234.60   $234.60  
  Purchase #4 $156.89   12.629%   $176.7036   $176.70   $176.70   $176.70  
  Purchase #5 $108.67   6.305%   $115.5216   $115.52   $115.50   $115.50  
  Purchase #6 $184.49   3.775%   $191.4545   $191.45   $191.45   $191.50  
  Purchase #7 $137.30   9.707%   $150.6277   $150.63   $150.65   $150.60  
  7 purchase totals = $993.04       $1,091.9345   $1,091.92   $1,091.90   $1,091.90