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 $152.44   4.646%   $159.5224   $159.52   $159.50   $159.50  
  Purchase #2 $153.45   8.603%   $166.6513   $166.65   $166.65   $166.70  
  Purchase #3 $213.51   4.597%   $223.3251   $223.33   $223.35   $223.30  
  Purchase #4 $119.48   4.201%   $124.4994   $124.50   $124.50   $124.50  
  Purchase #5 $165.98   7.775%   $178.8849   $178.88   $178.90   $178.90  
  Purchase #6 $130.82   4.579%   $136.8102   $136.81   $136.80   $136.80  
  Purchase #7 $168.67   4.842%   $176.837   $176.84   $176.85   $176.80  
  7 purchase totals = $1,104.35       $1,166.5303   $1,166.53   $1,166.55   $1,166.50