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 $67.81   9.486%   $74.2425   $74.24   $74.25   $74.20  
  Purchase #2 $186.64   6.486%   $198.7455   $198.75   $198.75   $198.70  
  Purchase #3 $179.61   13.629%   $204.089   $204.09   $204.10   $204.10  
  Purchase #4 $36.77   13.345%   $41.677   $41.68   $41.70   $41.70  
  Purchase #5 $8.32   6.158%   $8.8323   $8.83   $8.85   $8.80  
  Purchase #6 $205.52   5.281%   $216.3735   $216.37   $216.35   $216.40  
  Purchase #7 $225.90   3.141%   $232.9955   $233.00   $233.00   $233.00  
  7 purchase totals = $910.57       $976.9553   $976.96   $977.00   $976.90