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 $201.43   10.512%   $222.6043   $222.60   $222.60   $222.60  
  Purchase #2 $46.60   12.295%   $52.3295   $52.33   $52.35   $52.30  
  Purchase #3 $174.93   10.625%   $193.5163   $193.52   $193.50   $193.50  
  Purchase #4 $192.92   5.212%   $202.975   $202.98   $203.00   $203.00  
  Purchase #5 $210.72   13.439%   $239.0387   $239.04   $239.05   $239.00  
  Purchase #6 $30.45   11.652%   $33.998   $34.00   $34.00   $34.00  
  Purchase #7 $242.53   8.296%   $262.6503   $262.65   $262.65   $262.70  
  7 purchase totals = $1,099.58       $1,207.1121   $1,207.12   $1,207.15   $1,207.10