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 $124.62   13.453%   $141.3851   $141.39   $141.40   $141.40  
  Purchase #2 $85.54   13.227%   $96.8544   $96.85   $96.85   $96.90  
  Purchase #3 $72.71   6.424%   $77.3809   $77.38   $77.40   $77.40  
  Purchase #4 $67.50   5.600%   $71.28   $71.28   $71.30   $71.30  
  Purchase #5 $243.94   11.521%   $272.0443   $272.04   $272.05   $272.00  
  Purchase #6 $24.27   10.499%   $26.8181   $26.82   $26.80   $26.80  
  Purchase #7 $113.50   11.308%   $126.3346   $126.33   $126.35   $126.30  
  7 purchase totals = $732.08       $812.0974   $812.09   $812.15   $812.10