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 $124.97   13.592%   $141.9559   $141.96   $141.95   $142.00  
  Purchase #2 $213.41   10.417%   $235.6409   $235.64   $235.65   $235.60  
  Purchase #3 $148.90   9.216%   $162.6226   $162.62   $162.60   $162.60  
  Purchase #4 $243.83   11.300%   $271.3828   $271.38   $271.40   $271.40  
  Purchase #5 $99.50   3.155%   $102.6392   $102.64   $102.65   $102.60  
  Purchase #6 $76.81   12.690%   $86.5572   $86.56   $86.55   $86.60  
  Purchase #7 $176.49   8.667%   $191.7864   $191.79   $191.80   $191.80  
  7 purchase totals = $1,083.91       $1,192.5850   $1,192.59   $1,192.60   $1,192.60