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 $211.52   13.513%   $240.1027   $240.10   $240.10   $240.10  
  Purchase #2 $113.88   4.256%   $118.7267   $118.73   $118.75   $118.70  
  Purchase #3 $59.66   10.591%   $65.9786   $65.98   $66.00   $66.00  
  Purchase #4 $26.78   10.400%   $29.5651   $29.57   $29.55   $29.60  
  Purchase #5 $90.54   5.220%   $95.2662   $95.27   $95.25   $95.30  
  Purchase #6 $58.72   12.234%   $65.9038   $65.90   $65.90   $65.90  
  Purchase #7 $83.67   13.746%   $95.1713   $95.17   $95.15   $95.20  
  7 purchase totals = $644.77       $710.7144   $710.72   $710.70   $710.80