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 $61.85   8.224%   $66.9365   $66.94   $66.95   $66.90  
  Purchase #2 $217.31   13.307%   $246.2274   $246.23   $246.25   $246.20  
  Purchase #3 $88.50   9.200%   $96.642   $96.64   $96.65   $96.60  
  Purchase #4 $237.70   7.219%   $254.8596   $254.86   $254.85   $254.90  
  Purchase #5 $116.51   4.860%   $122.1724   $122.17   $122.15   $122.20  
  Purchase #6 $215.89   13.589%   $245.2273   $245.23   $245.25   $245.20  
  Purchase #7 $5.95   11.469%   $6.6324   $6.63   $6.65   $6.60  
  7 purchase totals = $943.71       $1,038.6976   $1,038.70   $1,038.75   $1,038.60