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 $196.46   3.280%   $202.9039   $202.90   $202.90   $202.90  
  Purchase #2 $73.93   9.147%   $80.6924   $80.69   $80.70   $80.70  
  Purchase #3 $20.34   4.852%   $21.3269   $21.33   $21.35   $21.30  
  Purchase #4 $57.55   12.145%   $64.5394   $64.54   $64.55   $64.50  
  Purchase #5 $22.90   13.249%   $25.934   $25.93   $25.95   $25.90  
  Purchase #6 $125.85   13.805%   $143.2236   $143.22   $143.20   $143.20  
  Purchase #7 $194.74   5.367%   $205.1917   $205.19   $205.20   $205.20  
  7 purchase totals = $691.77       $743.8119   $743.80   $743.85   $743.70