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 $118.76   12.870%   $134.0444   $134.04   $134.05   $134.00  
  Purchase #2 $7.59   6.181%   $8.0591   $8.06   $8.05   $8.10  
  Purchase #3 $46.95   8.140%   $50.7717   $50.77   $50.75   $50.80  
  Purchase #4 $30.63   4.438%   $31.9894   $31.99   $32.00   $32.00  
  Purchase #5 $130.90   9.540%   $143.3879   $143.39   $143.40   $143.40  
  Purchase #6 $160.53   4.435%   $167.6495   $167.65   $167.65   $167.60  
  Purchase #7 $50.55   11.803%   $56.5164   $56.52   $56.50   $56.50  
  7 purchase totals = $545.91       $592.4184   $592.42   $592.40   $592.40