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 $181.38   12.793%   $204.5839   $204.58   $204.60   $204.60  
  Purchase #2 $244.90   9.769%   $268.8243   $268.82   $268.80   $268.80  
  Purchase #3 $221.55   13.253%   $250.912   $250.91   $250.90   $250.90  
  Purchase #4 $219.76   11.597%   $245.2456   $245.25   $245.25   $245.20  
  Purchase #5 $97.79   5.261%   $102.9347   $102.93   $102.95   $102.90  
  Purchase #6 $80.47   7.668%   $86.6404   $86.64   $86.65   $86.60  
  Purchase #7 $69.70   5.656%   $73.6422   $73.64   $73.65   $73.60  
  7 purchase totals = $1,115.55       $1,232.7831   $1,232.77   $1,232.80   $1,232.60