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 $238.83   7.704%   $257.2295   $257.23   $257.25   $257.20  
  Purchase #2 $209.38   6.121%   $222.1961   $222.20   $222.20   $222.20  
  Purchase #3 $106.53   12.670%   $120.0274   $120.03   $120.05   $120.00  
  Purchase #4 $95.99   7.688%   $103.3697   $103.37   $103.35   $103.40  
  Purchase #5 $195.28   6.278%   $207.5397   $207.54   $207.55   $207.50  
  Purchase #6 $220.29   4.427%   $230.0422   $230.04   $230.05   $230.00  
  Purchase #7 $12.76   8.765%   $13.8784   $13.88   $13.90   $13.90  
  7 purchase totals = $1,079.06       $1,154.2830   $1,154.29   $1,154.35   $1,154.20