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 $224.42   13.564%   $254.8603   $254.86   $254.85   $254.90  
  Purchase #2 $145.57   12.394%   $163.6119   $163.61   $163.60   $163.60  
  Purchase #3 $187.92   8.274%   $203.4685   $203.47   $203.45   $203.50  
  Purchase #4 $158.42   4.493%   $165.5378   $165.54   $165.55   $165.50  
  Purchase #5 $120.81   12.144%   $135.4812   $135.48   $135.50   $135.50  
  Purchase #6 $36.76   11.524%   $40.9962   $41.00   $41.00   $41.00  
  Purchase #7 $80.77   9.114%   $88.1314   $88.13   $88.15   $88.10  
  7 purchase totals = $954.67       $1,052.0873   $1,052.09   $1,052.10   $1,052.10