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 $76.69   11.583%   $85.573   $85.57   $85.55   $85.60  
  Purchase #2 $128.71   4.239%   $134.166   $134.17   $134.15   $134.20  
  Purchase #3 $209.32   11.261%   $232.8915   $232.89   $232.90   $232.90  
  Purchase #4 $196.46   7.363%   $210.9253   $210.93   $210.95   $210.90  
  Purchase #5 $244.79   7.848%   $264.0011   $264.00   $264.00   $264.00  
  Purchase #6 $230.82   9.199%   $252.0531   $252.05   $252.05   $252.10  
  Purchase #7 $198.79   7.605%   $213.908   $213.91   $213.90   $213.90  
  7 purchase totals = $1,285.58       $1,393.5180   $1,393.52   $1,393.50   $1,393.60