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 $217.86   13.355%   $246.9552   $246.96   $246.95   $247.00  
  Purchase #2 $79.38   3.204%   $81.9233   $81.92   $81.90   $81.90  
  Purchase #3 $21.98   8.714%   $23.8953   $23.90   $23.90   $23.90  
  Purchase #4 $26.66   11.752%   $29.7931   $29.79   $29.80   $29.80  
  Purchase #5 $219.41   3.215%   $226.464   $226.46   $226.45   $226.50  
  Purchase #6 $175.81   12.376%   $197.5682   $197.57   $197.55   $197.60  
  Purchase #7 $65.68   3.653%   $68.0793   $68.08   $68.10   $68.10  
  7 purchase totals = $806.78       $874.6784   $874.68   $874.65   $874.80