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 $121.84   12.647%   $137.2491   $137.25   $137.25   $137.20  
  Purchase #2 $174.97   6.107%   $185.6554   $185.66   $185.65   $185.70  
  Purchase #3 $133.91   10.280%   $147.6759   $147.68   $147.70   $147.70  
  Purchase #4 $115.46   10.448%   $127.5233   $127.52   $127.50   $127.50  
  Purchase #5 $127.52   4.407%   $133.1398   $133.14   $133.15   $133.10  
  Purchase #6 $163.67   5.587%   $172.8142   $172.81   $172.80   $172.80  
  Purchase #7 $125.70   11.427%   $140.0637   $140.06   $140.05   $140.10  
  7 purchase totals = $963.07       $1,044.1214   $1,044.12   $1,044.10   $1,044.10