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 $34.60   7.351%   $37.1434   $37.14   $37.15   $37.10  
  Purchase #2 $10.37   10.439%   $11.4525   $11.45   $11.45   $11.50  
  Purchase #3 $23.94   4.449%   $25.0051   $25.01   $25.00   $25.00  
  Purchase #4 $52.79   13.602%   $59.9705   $59.97   $59.95   $60.00  
  Purchase #5 $224.26   5.820%   $237.3119   $237.31   $237.30   $237.30  
  Purchase #6 $182.60   12.555%   $205.5254   $205.53   $205.55   $205.50  
  Purchase #7 $145.89   8.224%   $157.888   $157.89   $157.90   $157.90  
  7 purchase totals = $674.45       $734.2968   $734.30   $734.30   $734.30