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 $58.25   13.405%   $66.0584   $66.06   $66.05   $66.10  
  Purchase #2 $69.48   11.718%   $77.6217   $77.62   $77.60   $77.60  
  Purchase #3 $84.37   13.728%   $95.9523   $95.95   $95.95   $96.00  
  Purchase #4 $135.89   13.155%   $153.7663   $153.77   $153.75   $153.80  
  Purchase #5 $106.62   10.441%   $117.7522   $117.75   $117.75   $117.80  
  Purchase #6 $226.52   8.481%   $245.7312   $245.73   $245.75   $245.70  
  Purchase #7 $122.29   13.417%   $138.6976   $138.70   $138.70   $138.70  
  7 purchase totals = $803.42       $895.5797   $895.58   $895.55   $895.70