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 $136.90   9.811%   $150.3313   $150.33   $150.35   $150.30  
  Purchase #2 $244.80   7.307%   $262.6875   $262.69   $262.70   $262.70  
  Purchase #3 $176.70   10.339%   $194.969   $194.97   $194.95   $195.00  
  Purchase #4 $151.49   13.563%   $172.0366   $172.04   $172.05   $172.00  
  Purchase #5 $207.29   13.467%   $235.2057   $235.21   $235.20   $235.20  
  Purchase #6 $26.47   6.794%   $28.2684   $28.27   $28.25   $28.30  
  Purchase #7 $145.26   12.661%   $163.6514   $163.65   $163.65   $163.70  
  7 purchase totals = $1,088.91       $1,207.1499   $1,207.16   $1,207.15   $1,207.20