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 $57.68   12.570%   $64.9304   $64.93   $64.95   $64.90  
  Purchase #2 $198.58   4.873%   $208.2568   $208.26   $208.25   $208.30  
  Purchase #3 $48.45   4.427%   $50.5949   $50.59   $50.60   $50.60  
  Purchase #4 $21.33   7.651%   $22.962   $22.96   $22.95   $23.00  
  Purchase #5 $23.88   3.790%   $24.7851   $24.79   $24.80   $24.80  
  Purchase #6 $247.83   3.406%   $256.2711   $256.27   $256.25   $256.30  
  Purchase #7 $110.32   11.717%   $123.2462   $123.25   $123.25   $123.20  
  7 purchase totals = $708.07       $751.0465   $751.05   $751.05   $751.10