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 $223.99   13.690%   $254.6542   $254.65   $254.65   $254.70  
  Purchase #2 $152.38   7.324%   $163.5403   $163.54   $163.55   $163.50  
  Purchase #3 $127.74   6.196%   $135.6548   $135.65   $135.65   $135.70  
  Purchase #4 $13.53   7.554%   $14.5521   $14.55   $14.55   $14.60  
  Purchase #5 $113.80   8.310%   $123.2568   $123.26   $123.25   $123.30  
  Purchase #6 $124.54   11.560%   $138.9368   $138.94   $138.95   $138.90  
  Purchase #7 $123.63   12.280%   $138.8118   $138.81   $138.80   $138.80  
  7 purchase totals = $879.61       $969.4068   $969.40   $969.40   $969.50