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 $248.76   11.119%   $276.4196   $276.42   $276.40   $276.40  
  Purchase #2 $33.94   10.305%   $37.4375   $37.44   $37.45   $37.40  
  Purchase #3 $183.61   3.254%   $189.5847   $189.58   $189.60   $189.60  
  Purchase #4 $12.40   6.586%   $13.2167   $13.22   $13.20   $13.20  
  Purchase #5 $180.98   11.164%   $201.1846   $201.18   $201.20   $201.20  
  Purchase #6 $135.65   12.571%   $152.7026   $152.70   $152.70   $152.70  
  Purchase #7 $152.58   7.363%   $163.8145   $163.81   $163.80   $163.80  
  7 purchase totals = $947.92       $1,034.3602   $1,034.35   $1,034.35   $1,034.30