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 $62.34   12.661%   $70.2329   $70.23   $70.25   $70.20  
  Purchase #2 $108.40   10.346%   $119.6151   $119.62   $119.60   $119.60  
  Purchase #3 $52.94   10.343%   $58.4156   $58.42   $58.40   $58.40  
  Purchase #4 $235.79   5.270%   $248.2161   $248.22   $248.20   $248.20  
  Purchase #5 $151.45   6.646%   $161.5154   $161.52   $161.50   $161.50  
  Purchase #6 $175.67   11.643%   $196.1233   $196.12   $196.10   $196.10  
  Purchase #7 $62.43   10.186%   $68.7891   $68.79   $68.80   $68.80  
  7 purchase totals = $849.02       $922.9075   $922.92   $922.85   $922.80