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 $239.49   10.466%   $264.555   $264.56   $264.55   $264.60  
  Purchase #2 $57.48   6.494%   $61.2128   $61.21   $61.20   $61.20  
  Purchase #3 $40.82   10.187%   $44.9783   $44.98   $45.00   $45.00  
  Purchase #4 $68.83   11.154%   $76.5073   $76.51   $76.50   $76.50  
  Purchase #5 $203.60   8.310%   $220.5192   $220.52   $220.50   $220.50  
  Purchase #6 $43.72   5.145%   $45.9694   $45.97   $45.95   $46.00  
  Purchase #7 $34.62   8.724%   $37.6402   $37.64   $37.65   $37.60  
  7 purchase totals = $688.56       $751.3822   $751.39   $751.35   $751.40