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 $70.97   3.371%   $73.3624   $73.36   $73.35   $73.40  
  Purchase #2 $140.96   8.839%   $153.4195   $153.42   $153.40   $153.40  
  Purchase #3 $45.54   5.478%   $48.0347   $48.03   $48.05   $48.00  
  Purchase #4 $169.33   10.813%   $187.6397   $187.64   $187.65   $187.60  
  Purchase #5 $212.43   9.163%   $231.895   $231.90   $231.90   $231.90  
  Purchase #6 $188.64   12.368%   $211.971   $211.97   $211.95   $212.00  
  Purchase #7 $78.28   13.484%   $88.8353   $88.84   $88.85   $88.80  
  7 purchase totals = $906.15       $995.1576   $995.16   $995.15   $995.10