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 $93.46   3.578%   $96.804   $96.80   $96.80   $96.80  
  Purchase #2 $43.36   4.587%   $45.3489   $45.35   $45.35   $45.30  
  Purchase #3 $103.68   7.455%   $111.4093   $111.41   $111.40   $111.40  
  Purchase #4 $41.30   8.291%   $44.7242   $44.72   $44.70   $44.70  
  Purchase #5 $164.82   13.402%   $186.9092   $186.91   $186.90   $186.90  
  Purchase #6 $235.29   4.839%   $246.6757   $246.68   $246.70   $246.70  
  Purchase #7 $194.41   8.125%   $210.2058   $210.21   $210.20   $210.20  
  7 purchase totals = $876.32       $942.0771   $942.08   $942.05   $942.00