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 $189.64   3.828%   $196.8994   $196.90   $196.90   $196.90  
  Purchase #2 $153.34   3.270%   $158.3542   $158.35   $158.35   $158.40  
  Purchase #3 $67.93   11.824%   $75.962   $75.96   $75.95   $76.00  
  Purchase #4 $177.72   13.617%   $201.9201   $201.92   $201.90   $201.90  
  Purchase #5 $55.63   3.676%   $57.675   $57.68   $57.70   $57.70  
  Purchase #6 $104.89   4.107%   $109.1978   $109.20   $109.20   $109.20  
  Purchase #7 $127.75   8.310%   $138.366   $138.37   $138.35   $138.40  
  7 purchase totals = $876.90       $938.3745   $938.38   $938.35   $938.50