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 $10.26   9.443%   $11.2289   $11.23   $11.25   $11.20  
  Purchase #2 $217.57   6.627%   $231.9884   $231.99   $232.00   $232.00  
  Purchase #3 $143.80   6.388%   $152.9859   $152.99   $153.00   $153.00  
  Purchase #4 $137.45   9.828%   $150.9586   $150.96   $150.95   $151.00  
  Purchase #5 $65.90   13.422%   $74.7451   $74.75   $74.75   $74.70  
  Purchase #6 $186.73   4.307%   $194.7725   $194.77   $194.75   $194.80  
  Purchase #7 $188.34   11.458%   $209.92   $209.92   $209.90   $209.90  
  7 purchase totals = $950.05       $1,026.5994   $1,026.61   $1,026.60   $1,026.60