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 $62.52   6.693%   $66.7045   $66.70   $66.70   $66.70  
  Purchase #2 $149.55   7.395%   $160.6092   $160.61   $160.60   $160.60  
  Purchase #3 $142.28   12.433%   $159.9697   $159.97   $159.95   $160.00  
  Purchase #4 $47.67   10.418%   $52.6363   $52.64   $52.65   $52.60  
  Purchase #5 $173.99   10.290%   $191.8936   $191.89   $191.90   $191.90  
  Purchase #6 $66.33   4.623%   $69.3964   $69.40   $69.40   $69.40  
  Purchase #7 $136.49   6.601%   $145.4997   $145.50   $145.50   $145.50  
  7 purchase totals = $778.83       $846.7094   $846.71   $846.70   $846.70