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 $11.31   10.658%   $12.5154   $12.52   $12.50   $12.50  
  Purchase #2 $245.87   12.701%   $277.0979   $277.10   $277.10   $277.10  
  Purchase #3 $55.52   5.675%   $58.6708   $58.67   $58.65   $58.70  
  Purchase #4 $119.68   13.254%   $135.5424   $135.54   $135.55   $135.50  
  Purchase #5 $12.35   5.246%   $12.9979   $13.00   $13.00   $13.00  
  Purchase #6 $58.64   4.585%   $61.3286   $61.33   $61.35   $61.30  
  Purchase #7 $105.34   11.704%   $117.669   $117.67   $117.65   $117.70  
  7 purchase totals = $608.71       $675.8220   $675.83   $675.80   $675.80