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 $93.67   8.824%   $101.9354   $101.94   $101.95   $101.90  
  Purchase #2 $145.75   4.511%   $152.3248   $152.32   $152.30   $152.30  
  Purchase #3 $134.35   9.541%   $147.1683   $147.17   $147.15   $147.20  
  Purchase #4 $199.60   13.483%   $226.5121   $226.51   $226.50   $226.50  
  Purchase #5 $5.52   8.210%   $5.9732   $5.97   $5.95   $6.00  
  Purchase #6 $157.76   5.319%   $166.1513   $166.15   $166.15   $166.20  
  Purchase #7 $64.27   12.626%   $72.3847   $72.38   $72.40   $72.40  
  7 purchase totals = $800.92       $872.4498   $872.44   $872.40   $872.50