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 $220.26   8.740%   $239.5107   $239.51   $239.50   $239.50  
  Purchase #2 $49.36   10.740%   $54.6613   $54.66   $54.65   $54.70  
  Purchase #3 $83.88   3.253%   $86.6086   $86.61   $86.60   $86.60  
  Purchase #4 $182.53   10.350%   $201.4219   $201.42   $201.40   $201.40  
  Purchase #5 $86.89   10.252%   $95.798   $95.80   $95.80   $95.80  
  Purchase #6 $182.51   12.129%   $204.6466   $204.65   $204.65   $204.60  
  Purchase #7 $161.80   3.485%   $167.4387   $167.44   $167.45   $167.40  
  7 purchase totals = $967.23       $1,050.0858   $1,050.09   $1,050.05   $1,050.00