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 $31.35   10.308%   $34.5816   $34.58   $34.60   $34.60  
  Purchase #2 $143.42   4.122%   $149.3318   $149.33   $149.35   $149.30  
  Purchase #3 $26.43   6.704%   $28.2019   $28.20   $28.20   $28.20  
  Purchase #4 $70.59   8.715%   $76.7419   $76.74   $76.75   $76.70  
  Purchase #5 $56.86   5.494%   $59.9839   $59.98   $60.00   $60.00  
  Purchase #6 $200.37   6.604%   $213.6024   $213.60   $213.60   $213.60  
  Purchase #7 $128.89   6.222%   $136.9095   $136.91   $136.90   $136.90  
  7 purchase totals = $657.91       $699.3530   $699.34   $699.40   $699.30