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 $63.45   12.623%   $71.4593   $71.46   $71.45   $71.50  
  Purchase #2 $47.67   3.687%   $49.4276   $49.43   $49.45   $49.40  
  Purchase #3 $243.58   12.173%   $273.231   $273.23   $273.25   $273.20  
  Purchase #4 $192.51   6.255%   $204.5515   $204.55   $204.55   $204.60  
  Purchase #5 $42.58   12.122%   $47.7415   $47.74   $47.75   $47.70  
  Purchase #6 $62.56   4.349%   $65.2807   $65.28   $65.30   $65.30  
  Purchase #7 $126.35   11.345%   $140.6844   $140.68   $140.70   $140.70  
  7 purchase totals = $778.70       $852.3760   $852.37   $852.45   $852.40