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 $158.76   5.652%   $167.7331   $167.73   $167.75   $167.70  
  Purchase #2 $115.58   6.397%   $122.9737   $122.97   $122.95   $123.00  
  Purchase #3 $106.52   10.168%   $117.351   $117.35   $117.35   $117.40  
  Purchase #4 $116.86   9.760%   $128.2655   $128.27   $128.25   $128.30  
  Purchase #5 $175.55   5.779%   $185.695   $185.70   $185.70   $185.70  
  Purchase #6 $24.91   8.434%   $27.0109   $27.01   $27.00   $27.00  
  Purchase #7 $225.34   8.157%   $243.721   $243.72   $243.70   $243.70  
  7 purchase totals = $923.52       $992.7502   $992.75   $992.70   $992.80