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 $98.33   10.585%   $108.7382   $108.74   $108.75   $108.70  
  Purchase #2 $201.83   8.295%   $218.5718   $218.57   $218.55   $218.60  
  Purchase #3 $192.66   6.765%   $205.6934   $205.69   $205.70   $205.70  
  Purchase #4 $166.39   5.194%   $175.0323   $175.03   $175.05   $175.00  
  Purchase #5 $120.69   9.156%   $131.7404   $131.74   $131.75   $131.70  
  Purchase #6 $195.47   6.386%   $207.9527   $207.95   $207.95   $208.00  
  Purchase #7 $223.66   12.591%   $251.821   $251.82   $251.80   $251.80  
  7 purchase totals = $1,199.03       $1,299.5498   $1,299.54   $1,299.55   $1,299.50