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 $62.51   10.351%   $68.9804   $68.98   $69.00   $69.00  
  Purchase #2 $124.82   8.304%   $135.1851   $135.19   $135.20   $135.20  
  Purchase #3 $150.95   13.749%   $171.7041   $171.70   $171.70   $171.70  
  Purchase #4 $238.59   8.705%   $259.3593   $259.36   $259.35   $259.40  
  Purchase #5 $67.75   12.527%   $76.237   $76.24   $76.25   $76.20  
  Purchase #6 $97.79   8.439%   $106.0425   $106.04   $106.05   $106.00  
  Purchase #7 $82.44   3.653%   $85.4515   $85.45   $85.45   $85.50  
  7 purchase totals = $824.85       $902.9599   $902.96   $903.00   $903.00