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 $56.40   9.362%   $61.6802   $61.68   $61.70   $61.70  
  Purchase #2 $194.97   13.692%   $221.6653   $221.67   $221.65   $221.70  
  Purchase #3 $85.28   13.563%   $96.8465   $96.85   $96.85   $96.80  
  Purchase #4 $83.81   12.545%   $94.324   $94.32   $94.30   $94.30  
  Purchase #5 $182.26   12.380%   $204.8238   $204.82   $204.80   $204.80  
  Purchase #6 $28.45   5.267%   $29.9485   $29.95   $29.95   $29.90  
  Purchase #7 $71.97   6.112%   $76.3688   $76.37   $76.35   $76.40  
  7 purchase totals = $703.14       $785.6571   $785.66   $785.60   $785.60