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 $89.55   9.606%   $98.1522   $98.15   $98.15   $98.20  
  Purchase #2 $23.87   11.703%   $26.6635   $26.66   $26.65   $26.70  
  Purchase #3 $240.28   8.220%   $260.031   $260.03   $260.05   $260.00  
  Purchase #4 $248.77   3.277%   $256.9222   $256.92   $256.90   $256.90  
  Purchase #5 $142.94   8.421%   $154.977   $154.98   $155.00   $155.00  
  Purchase #6 $51.52   9.519%   $56.4242   $56.42   $56.40   $56.40  
  Purchase #7 $102.99   7.451%   $110.6638   $110.66   $110.65   $110.70  
  7 purchase totals = $899.92       $963.8339   $963.82   $963.80   $963.90