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 $65.75   7.280%   $70.5366   $70.54   $70.55   $70.50  
  Purchase #2 $191.95   7.562%   $206.4653   $206.47   $206.45   $206.50  
  Purchase #3 $152.44   8.560%   $165.4889   $165.49   $165.50   $165.50  
  Purchase #4 $79.52   4.311%   $82.9481   $82.95   $82.95   $82.90  
  Purchase #5 $207.50   5.189%   $218.2672   $218.27   $218.25   $218.30  
  Purchase #6 $94.86   10.314%   $104.6439   $104.64   $104.65   $104.60  
  Purchase #7 $169.94   13.675%   $193.1793   $193.18   $193.20   $193.20  
  7 purchase totals = $961.96       $1,041.5293   $1,041.54   $1,041.55   $1,041.50