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 $241.26   7.459%   $259.2556   $259.26   $259.25   $259.30  
  Purchase #2 $120.29   5.196%   $126.5403   $126.54   $126.55   $126.50  
  Purchase #3 $190.49   8.745%   $207.1484   $207.15   $207.15   $207.10  
  Purchase #4 $94.70   8.190%   $102.4559   $102.46   $102.45   $102.50  
  Purchase #5 $142.39   13.158%   $161.1257   $161.13   $161.15   $161.10  
  Purchase #6 $138.42   13.621%   $157.2742   $157.27   $157.25   $157.30  
  Purchase #7 $85.68   9.513%   $93.8307   $93.83   $93.85   $93.80  
  7 purchase totals = $1,013.23       $1,107.6308   $1,107.64   $1,107.65   $1,107.60