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 $153.76   7.210%   $164.8461   $164.85   $164.85   $164.80  
  Purchase #2 $110.98   6.852%   $118.5843   $118.58   $118.60   $118.60  
  Purchase #3 $60.51   3.809%   $62.8148   $62.81   $62.80   $62.80  
  Purchase #4 $233.77   4.400%   $244.0559   $244.06   $244.05   $244.10  
  Purchase #5 $115.89   8.301%   $125.51   $125.51   $125.50   $125.50  
  Purchase #6 $145.52   3.768%   $151.0032   $151.00   $151.00   $151.00  
  Purchase #7 $15.55   3.719%   $16.1283   $16.13   $16.15   $16.10  
  7 purchase totals = $835.98       $882.9426   $882.94   $882.95   $882.90