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 $188.79   13.747%   $214.743   $214.74   $214.75   $214.70  
  Purchase #2 $56.27   11.235%   $62.5919   $62.59   $62.60   $62.60  
  Purchase #3 $38.30   4.497%   $40.0224   $40.02   $40.00   $40.00  
  Purchase #4 $247.44   10.250%   $272.8026   $272.80   $272.80   $272.80  
  Purchase #5 $56.47   6.427%   $60.0993   $60.10   $60.10   $60.10  
  Purchase #6 $229.92   7.654%   $247.5181   $247.52   $247.50   $247.50  
  Purchase #7 $39.62   11.865%   $44.3209   $44.32   $44.30   $44.30  
  7 purchase totals = $856.81       $942.0982   $942.09   $942.05   $942.00