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 $5.88   3.581%   $6.0906   $6.09   $6.10   $6.10  
  Purchase #2 $85.82   11.372%   $95.5795   $95.58   $95.60   $95.60  
  Purchase #3 $5.67   3.403%   $5.863   $5.86   $5.85   $5.90  
  Purchase #4 $62.52   9.865%   $68.6876   $68.69   $68.70   $68.70  
  Purchase #5 $66.92   13.361%   $75.8612   $75.86   $75.85   $75.90  
  Purchase #6 $225.83   5.811%   $238.953   $238.95   $238.95   $239.00  
  Purchase #7 $62.79   11.382%   $69.9368   $69.94   $69.95   $69.90  
  7 purchase totals = $515.43       $560.9717   $560.97   $561.00   $561.10