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 $37.61   13.588%   $42.7204   $42.72   $42.70   $42.70  
  Purchase #2 $214.50   9.769%   $235.4545   $235.45   $235.45   $235.50  
  Purchase #3 $200.43   9.532%   $219.535   $219.54   $219.55   $219.50  
  Purchase #4 $155.66   13.555%   $176.7597   $176.76   $176.75   $176.80  
  Purchase #5 $204.74   6.702%   $218.4617   $218.46   $218.45   $218.50  
  Purchase #6 $184.40   10.658%   $204.0534   $204.05   $204.05   $204.10  
  Purchase #7 $26.44   4.164%   $27.541   $27.54   $27.55   $27.50  
  7 purchase totals = $1,023.78       $1,124.5257   $1,124.52   $1,124.50   $1,124.60