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 $86.88   7.254%   $93.1823   $93.18   $93.20   $93.20  
  Purchase #2 $70.28   5.381%   $74.0618   $74.06   $74.05   $74.10  
  Purchase #3 $95.60   10.377%   $105.5204   $105.52   $105.50   $105.50  
  Purchase #4 $136.50   10.412%   $150.7124   $150.71   $150.70   $150.70  
  Purchase #5 $190.88   5.795%   $201.9415   $201.94   $201.95   $201.90  
  Purchase #6 $186.36   10.355%   $205.6576   $205.66   $205.65   $205.70  
  Purchase #7 $158.34   3.716%   $164.2239   $164.22   $164.20   $164.20  
  7 purchase totals = $924.84       $995.2999   $995.29   $995.25   $995.30