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 $56.67   8.554%   $61.5176   $61.52   $61.50   $61.50  
  Purchase #2 $167.95   8.591%   $182.3786   $182.38   $182.40   $182.40  
  Purchase #3 $148.61   10.323%   $163.951   $163.95   $163.95   $164.00  
  Purchase #4 $232.84   13.589%   $264.4806   $264.48   $264.50   $264.50  
  Purchase #5 $150.46   11.480%   $167.7328   $167.73   $167.75   $167.70  
  Purchase #6 $145.83   3.516%   $150.9574   $150.96   $150.95   $151.00  
  Purchase #7 $28.51   5.220%   $29.9982   $30.00   $30.00   $30.00  
  7 purchase totals = $930.87       $1,021.0162   $1,021.02   $1,021.05   $1,021.10