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 $23.34   12.747%   $26.3151   $26.32   $26.30   $26.30  
  Purchase #2 $101.27   6.492%   $107.8444   $107.84   $107.85   $107.80  
  Purchase #3 $13.52   10.437%   $14.9311   $14.93   $14.95   $14.90  
  Purchase #4 $130.69   10.798%   $144.8019   $144.80   $144.80   $144.80  
  Purchase #5 $202.44   10.585%   $223.8683   $223.87   $223.85   $223.90  
  Purchase #6 $216.86   9.311%   $237.0518   $237.05   $237.05   $237.10  
  Purchase #7 $171.34   5.104%   $180.0852   $180.09   $180.10   $180.10  
  7 purchase totals = $859.46       $934.8978   $934.90   $934.90   $934.90