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 $52.38   12.582%   $58.9705   $58.97   $58.95   $59.00  
  Purchase #2 $226.83   8.653%   $246.4576   $246.46   $246.45   $246.50  
  Purchase #3 $227.90   11.160%   $253.3336   $253.33   $253.35   $253.30  
  Purchase #4 $228.86   11.570%   $255.3391   $255.34   $255.35   $255.30  
  Purchase #5 $26.53   4.708%   $27.779   $27.78   $27.80   $27.80  
  Purchase #6 $11.45   10.785%   $12.6849   $12.68   $12.70   $12.70  
  Purchase #7 $136.82   11.128%   $152.0453   $152.05   $152.05   $152.00  
  7 purchase totals = $910.77       $1,006.6100   $1,006.61   $1,006.65   $1,006.60