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 $234.62   13.707%   $266.7794   $266.78   $266.80   $266.80  
  Purchase #2 $55.32   13.843%   $62.9779   $62.98   $63.00   $63.00  
  Purchase #3 $67.93   11.793%   $75.941   $75.94   $75.95   $75.90  
  Purchase #4 $219.56   3.521%   $227.2907   $227.29   $227.30   $227.30  
  Purchase #5 $154.27   6.174%   $163.7946   $163.79   $163.80   $163.80  
  Purchase #6 $13.90   9.650%   $15.2414   $15.24   $15.25   $15.20  
  Purchase #7 $226.64   9.704%   $248.6331   $248.63   $248.65   $248.60  
  7 purchase totals = $972.24       $1,060.6581   $1,060.65   $1,060.75   $1,060.60