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 $64.81   3.413%   $67.022   $67.02   $67.00   $67.00  
  Purchase #2 $9.31   13.169%   $10.536   $10.54   $10.55   $10.50  
  Purchase #3 $211.90   12.830%   $239.0868   $239.09   $239.10   $239.10  
  Purchase #4 $190.53   9.852%   $209.301   $209.30   $209.30   $209.30  
  Purchase #5 $158.65   6.483%   $168.9353   $168.94   $168.95   $168.90  
  Purchase #6 $204.36   4.206%   $212.9554   $212.96   $212.95   $213.00  
  Purchase #7 $149.53   3.537%   $154.8189   $154.82   $154.80   $154.80  
  7 purchase totals = $989.09       $1,062.6554   $1,062.67   $1,062.65   $1,062.60