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 $165.61   6.406%   $176.219   $176.22   $176.20   $176.20  
  Purchase #2 $76.79   6.213%   $81.561   $81.56   $81.55   $81.60  
  Purchase #3 $222.52   7.705%   $239.6652   $239.67   $239.65   $239.70  
  Purchase #4 $71.26   10.870%   $79.006   $79.01   $79.00   $79.00  
  Purchase #5 $95.33   13.827%   $108.5113   $108.51   $108.50   $108.50  
  Purchase #6 $126.99   11.838%   $142.0231   $142.02   $142.00   $142.00  
  Purchase #7 $187.72   5.749%   $198.512   $198.51   $198.50   $198.50  
  7 purchase totals = $946.22       $1,025.4976   $1,025.50   $1,025.40   $1,025.50