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 $181.25   3.153%   $186.9648   $186.96   $186.95   $187.00  
  Purchase #2 $154.27   3.722%   $160.0119   $160.01   $160.00   $160.00  
  Purchase #3 $246.52   8.677%   $267.9105   $267.91   $267.90   $267.90  
  Purchase #4 $224.40   8.397%   $243.2429   $243.24   $243.25   $243.20  
  Purchase #5 $71.63   3.767%   $74.3283   $74.33   $74.35   $74.30  
  Purchase #6 $226.78   7.202%   $243.1127   $243.11   $243.10   $243.10  
  Purchase #7 $248.31   10.628%   $274.7004   $274.70   $274.70   $274.70  
  7 purchase totals = $1,353.16       $1,450.2715   $1,450.26   $1,450.25   $1,450.20