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 $100.78   9.585%   $110.4398   $110.44   $110.45   $110.40  
  Purchase #2 $21.76   13.624%   $24.7246   $24.72   $24.70   $24.70  
  Purchase #3 $200.26   7.655%   $215.5899   $215.59   $215.60   $215.60  
  Purchase #4 $164.55   7.553%   $176.9785   $176.98   $177.00   $177.00  
  Purchase #5 $99.79   10.294%   $110.0624   $110.06   $110.05   $110.10  
  Purchase #6 $192.80   5.399%   $203.2093   $203.21   $203.20   $203.20  
  Purchase #7 $16.52   11.352%   $18.3954   $18.40   $18.40   $18.40  
  7 purchase totals = $796.46       $859.3999   $859.40   $859.40   $859.40