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 $176.53   10.416%   $194.9174   $194.92   $194.90   $194.90  
  Purchase #2 $245.87   7.552%   $264.4381   $264.44   $264.45   $264.40  
  Purchase #3 $22.33   11.118%   $24.8126   $24.81   $24.80   $24.80  
  Purchase #4 $212.80   5.854%   $225.2573   $225.26   $225.25   $225.30  
  Purchase #5 $221.67   6.106%   $235.2052   $235.21   $235.20   $235.20  
  Purchase #6 $66.87   11.401%   $74.4938   $74.49   $74.50   $74.50  
  Purchase #7 $36.86   13.865%   $41.9706   $41.97   $41.95   $42.00  
  7 purchase totals = $982.93       $1,061.0950   $1,061.10   $1,061.05   $1,061.10