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 $81.36   13.338%   $92.2118   $92.21   $92.20   $92.20  
  Purchase #2 $184.82   9.252%   $201.9195   $201.92   $201.90   $201.90  
  Purchase #3 $168.57   8.144%   $182.2983   $182.30   $182.30   $182.30  
  Purchase #4 $159.52   13.174%   $180.5352   $180.54   $180.55   $180.50  
  Purchase #5 $58.35   3.653%   $60.4815   $60.48   $60.50   $60.50  
  Purchase #6 $94.94   3.255%   $98.0303   $98.03   $98.05   $98.00  
  Purchase #7 $168.80   12.801%   $190.4081   $190.41   $190.40   $190.40  
  7 purchase totals = $916.36       $1,005.8847   $1,005.89   $1,005.90   $1,005.80