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 $111.52   13.210%   $126.2518   $126.25   $126.25   $126.30  
  Purchase #2 $229.99   6.361%   $244.6197   $244.62   $244.60   $244.60  
  Purchase #3 $202.56   9.612%   $222.0301   $222.03   $222.05   $222.00  
  Purchase #4 $85.51   7.859%   $92.2302   $92.23   $92.25   $92.20  
  Purchase #5 $149.39   12.492%   $168.0518   $168.05   $168.05   $168.10  
  Purchase #6 $54.66   3.311%   $56.4698   $56.47   $56.45   $56.50  
  Purchase #7 $176.55   13.574%   $200.5149   $200.51   $200.50   $200.50  
  7 purchase totals = $1,010.18       $1,110.1683   $1,110.16   $1,110.15   $1,110.20