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 $119.64   12.418%   $134.4969   $134.50   $134.50   $134.50  
  Purchase #2 $139.87   8.556%   $151.8373   $151.84   $151.85   $151.80  
  Purchase #3 $225.57   13.555%   $256.146   $256.15   $256.15   $256.10  
  Purchase #4 $72.80   5.209%   $76.5922   $76.59   $76.60   $76.60  
  Purchase #5 $189.26   8.687%   $205.701   $205.70   $205.70   $205.70  
  Purchase #6 $49.63   12.789%   $55.9772   $55.98   $56.00   $56.00  
  Purchase #7 $41.96   9.751%   $46.0515   $46.05   $46.05   $46.10  
  7 purchase totals = $838.73       $926.8021   $926.81   $926.85   $926.80