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 $240.84   11.685%   $268.9822   $268.98   $269.00   $269.00  
  Purchase #2 $68.38   13.724%   $77.7645   $77.76   $77.75   $77.80  
  Purchase #3 $113.77   7.524%   $122.3301   $122.33   $122.35   $122.30  
  Purchase #4 $128.75   11.467%   $143.5138   $143.51   $143.50   $143.50  
  Purchase #5 $67.95   10.340%   $74.976   $74.98   $75.00   $75.00  
  Purchase #6 $161.31   10.779%   $178.6976   $178.70   $178.70   $178.70  
  Purchase #7 $160.61   13.840%   $182.8384   $182.84   $182.85   $182.80  
  7 purchase totals = $941.61       $1,049.1026   $1,049.10   $1,049.15   $1,049.10