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 $55.96   8.440%   $60.683   $60.68   $60.70   $60.70  
  Purchase #2 $202.98   8.805%   $220.8524   $220.85   $220.85   $220.90  
  Purchase #3 $164.40   5.700%   $173.7708   $173.77   $173.75   $173.80  
  Purchase #4 $67.43   7.278%   $72.3376   $72.34   $72.35   $72.30  
  Purchase #5 $218.96   10.542%   $242.0428   $242.04   $242.05   $242.00  
  Purchase #6 $187.46   13.463%   $212.6977   $212.70   $212.70   $212.70  
  Purchase #7 $69.89   13.810%   $79.5418   $79.54   $79.55   $79.50  
  7 purchase totals = $967.08       $1,061.9261   $1,061.92   $1,061.95   $1,061.90