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 $226.51   11.118%   $251.6934   $251.69   $251.70   $251.70  
  Purchase #2 $154.99   11.867%   $173.3827   $173.38   $173.40   $173.40  
  Purchase #3 $156.70   8.308%   $169.7186   $169.72   $169.70   $169.70  
  Purchase #4 $201.94   9.631%   $221.3888   $221.39   $221.40   $221.40  
  Purchase #5 $10.93   10.190%   $12.0438   $12.04   $12.05   $12.00  
  Purchase #6 $193.53   11.819%   $216.4033   $216.40   $216.40   $216.40  
  Purchase #7 $22.74   9.661%   $24.9369   $24.94   $24.95   $24.90  
  7 purchase totals = $967.34       $1,069.5675   $1,069.56   $1,069.60   $1,069.50