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 $159.52   10.350%   $176.0303   $176.03   $176.05   $176.00  
  Purchase #2 $232.72   11.665%   $259.8668   $259.87   $259.85   $259.90  
  Purchase #3 $196.91   3.788%   $204.369   $204.37   $204.35   $204.40  
  Purchase #4 $151.64   11.243%   $168.6889   $168.69   $168.70   $168.70  
  Purchase #5 $8.98   6.348%   $9.5501   $9.55   $9.55   $9.60  
  Purchase #6 $118.58   12.201%   $133.0479   $133.05   $133.05   $133.00  
  Purchase #7 $48.65   10.421%   $53.7198   $53.72   $53.70   $53.70  
  7 purchase totals = $917.00       $1,005.2728   $1,005.28   $1,005.25   $1,005.30