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 $50.86   10.679%   $56.2913   $56.29   $56.30   $56.30  
  Purchase #2 $52.25   6.848%   $55.8281   $55.83   $55.85   $55.80  
  Purchase #3 $55.71   9.420%   $60.9579   $60.96   $60.95   $61.00  
  Purchase #4 $249.45   4.403%   $260.4333   $260.43   $260.45   $260.40  
  Purchase #5 $201.47   4.833%   $211.207   $211.21   $211.20   $211.20  
  Purchase #6 $31.98   6.307%   $33.997   $34.00   $34.00   $34.00  
  Purchase #7 $67.35   7.334%   $72.2894   $72.29   $72.30   $72.30  
  7 purchase totals = $709.07       $751.0040   $751.01   $751.05   $751.00