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 $174.67   5.483%   $184.2472   $184.25   $184.25   $184.20  
  Purchase #2 $53.78   5.347%   $56.6556   $56.66   $56.65   $56.70  
  Purchase #3 $37.69   5.548%   $39.781   $39.78   $39.80   $39.80  
  Purchase #4 $86.39   11.553%   $96.3706   $96.37   $96.35   $96.40  
  Purchase #5 $207.29   4.201%   $215.9983   $216.00   $216.00   $216.00  
  Purchase #6 $184.49   10.856%   $204.5182   $204.52   $204.50   $204.50  
  Purchase #7 $175.89   5.606%   $185.7504   $185.75   $185.75   $185.80  
  7 purchase totals = $920.20       $983.3213   $983.33   $983.30   $983.40