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 $56.39   12.269%   $63.3085   $63.31   $63.30   $63.30  
  Purchase #2 $64.82   13.700%   $73.7003   $73.70   $73.70   $73.70  
  Purchase #3 $165.61   12.269%   $185.9287   $185.93   $185.95   $185.90  
  Purchase #4 $132.32   11.161%   $147.0882   $147.09   $147.10   $147.10  
  Purchase #5 $35.28   13.484%   $40.0372   $40.04   $40.05   $40.00  
  Purchase #6 $121.68   13.858%   $138.5424   $138.54   $138.55   $138.50  
  Purchase #7 $116.67   6.654%   $124.4332   $124.43   $124.45   $124.40  
  7 purchase totals = $692.77       $773.0385   $773.04   $773.10   $772.90