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 $88.89   8.727%   $96.6474   $96.65   $96.65   $96.60  
  Purchase #2 $39.51   11.342%   $43.9912   $43.99   $44.00   $44.00  
  Purchase #3 $58.70   5.426%   $61.8851   $61.89   $61.90   $61.90  
  Purchase #4 $180.36   9.677%   $197.8134   $197.81   $197.80   $197.80  
  Purchase #5 $165.46   8.863%   $180.1247   $180.12   $180.10   $180.10  
  Purchase #6 $193.87   13.467%   $219.9785   $219.98   $220.00   $220.00  
  Purchase #7 $249.29   9.332%   $272.5537   $272.55   $272.55   $272.60  
  7 purchase totals = $976.08       $1,072.9940   $1,072.99   $1,073.00   $1,073.00