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 $97.34   10.261%   $107.3281   $107.33   $107.35   $107.30  
  Purchase #2 $65.36   8.534%   $70.9378   $70.94   $70.95   $70.90  
  Purchase #3 $90.95   5.508%   $95.9595   $95.96   $95.95   $96.00  
  Purchase #4 $128.68   12.509%   $144.7766   $144.78   $144.80   $144.80  
  Purchase #5 $228.53   3.576%   $236.7022   $236.70   $236.70   $236.70  
  Purchase #6 $78.49   8.474%   $85.1412   $85.14   $85.15   $85.10  
  Purchase #7 $116.74   3.593%   $120.9345   $120.93   $120.95   $120.90  
  7 purchase totals = $806.09       $861.7799   $861.78   $861.85   $861.70