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 $132.98   13.757%   $151.2741   $151.27   $151.25   $151.30  
  Purchase #2 $229.81   12.309%   $258.0973   $258.10   $258.10   $258.10  
  Purchase #3 $182.48   6.273%   $193.927   $193.93   $193.95   $193.90  
  Purchase #4 $91.28   12.789%   $102.9538   $102.95   $102.95   $103.00  
  Purchase #5 $212.31   6.614%   $226.3522   $226.35   $226.35   $226.40  
  Purchase #6 $164.63   4.527%   $172.0828   $172.08   $172.10   $172.10  
  Purchase #7 $126.54   7.500%   $136.0305   $136.03   $136.05   $136.00  
  7 purchase totals = $1,140.03       $1,240.7177   $1,240.71   $1,240.75   $1,240.80