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 $58.58   9.236%   $63.9904   $63.99   $64.00   $64.00  
  Purchase #2 $49.30   7.511%   $53.0029   $53.00   $53.00   $53.00  
  Purchase #3 $20.77   9.471%   $22.7371   $22.74   $22.75   $22.70  
  Purchase #4 $92.71   5.524%   $97.8313   $97.83   $97.85   $97.80  
  Purchase #5 $54.98   10.689%   $60.8568   $60.86   $60.85   $60.90  
  Purchase #6 $205.77   13.669%   $233.8967   $233.90   $233.90   $233.90  
  Purchase #7 $85.98   9.342%   $94.0123   $94.01   $94.00   $94.00  
  7 purchase totals = $568.09       $626.3275   $626.33   $626.35   $626.30