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 $178.75   13.431%   $202.7579   $202.76   $202.75   $202.80  
  Purchase #2 $175.83   12.650%   $198.0725   $198.07   $198.05   $198.10  
  Purchase #3 $69.80   8.509%   $75.7393   $75.74   $75.75   $75.70  
  Purchase #4 $210.53   8.275%   $227.9514   $227.95   $227.95   $228.00  
  Purchase #5 $205.54   11.173%   $228.505   $228.51   $228.50   $228.50  
  Purchase #6 $100.71   8.759%   $109.5312   $109.53   $109.55   $109.50  
  Purchase #7 $115.42   9.135%   $125.9636   $125.96   $125.95   $126.00  
  7 purchase totals = $1,056.58       $1,168.5209   $1,168.52   $1,168.50   $1,168.60