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 $87.82   9.324%   $96.0083   $96.01   $96.00   $96.00  
  Purchase #2 $102.90   5.495%   $108.5544   $108.55   $108.55   $108.60  
  Purchase #3 $188.97   7.767%   $203.6473   $203.65   $203.65   $203.60  
  Purchase #4 $237.47   13.432%   $269.367   $269.37   $269.35   $269.40  
  Purchase #5 $104.25   9.180%   $113.8202   $113.82   $113.80   $113.80  
  Purchase #6 $73.67   8.112%   $79.6461   $79.65   $79.65   $79.60  
  Purchase #7 $24.25   12.685%   $27.3261   $27.33   $27.35   $27.30  
  7 purchase totals = $819.33       $898.3694   $898.38   $898.35   $898.30