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 $49.54   11.747%   $55.3595   $55.36   $55.35   $55.40  
  Purchase #2 $197.45   12.765%   $222.6545   $222.65   $222.65   $222.70  
  Purchase #3 $208.51   9.860%   $229.0691   $229.07   $229.05   $229.10  
  Purchase #4 $204.80   10.748%   $226.8119   $226.81   $226.80   $226.80  
  Purchase #5 $32.94   8.757%   $35.8246   $35.82   $35.80   $35.80  
  Purchase #6 $150.93   11.155%   $167.7662   $167.77   $167.75   $167.80  
  Purchase #7 $105.41   9.273%   $115.1847   $115.18   $115.20   $115.20  
  7 purchase totals = $949.58       $1,052.6705   $1,052.66   $1,052.60   $1,052.80