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 $65.74   12.484%   $73.947   $73.95   $73.95   $73.90  
  Purchase #2 $58.89   12.113%   $66.0233   $66.02   $66.00   $66.00  
  Purchase #3 $74.58   12.431%   $83.851   $83.85   $83.85   $83.90  
  Purchase #4 $17.75   12.212%   $19.9176   $19.92   $19.90   $19.90  
  Purchase #5 $171.40   12.294%   $192.4719   $192.47   $192.45   $192.50  
  Purchase #6 $157.52   7.873%   $169.9215   $169.92   $169.90   $169.90  
  Purchase #7 $146.62   6.868%   $156.6899   $156.69   $156.70   $156.70  
  7 purchase totals = $692.50       $762.8222   $762.82   $762.75   $762.80