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 $209.85   10.602%   $232.0983   $232.10   $232.10   $232.10  
  Purchase #2 $145.52   11.497%   $162.2504   $162.25   $162.25   $162.30  
  Purchase #3 $175.48   11.220%   $195.1689   $195.17   $195.15   $195.20  
  Purchase #4 $112.82   6.217%   $119.834   $119.83   $119.85   $119.80  
  Purchase #5 $102.95   10.679%   $113.944   $113.94   $113.95   $113.90  
  Purchase #6 $53.98   11.591%   $60.2368   $60.24   $60.25   $60.20  
  Purchase #7 $183.91   13.758%   $209.2123   $209.21   $209.20   $209.20  
  7 purchase totals = $984.51       $1,092.7447   $1,092.74   $1,092.75   $1,092.70