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 $183.32   6.333%   $194.9297   $194.93   $194.95   $194.90  
  Purchase #2 $23.34   8.304%   $25.2782   $25.28   $25.30   $25.30  
  Purchase #3 $153.44   5.520%   $161.9099   $161.91   $161.90   $161.90  
  Purchase #4 $205.42   12.610%   $231.3235   $231.32   $231.30   $231.30  
  Purchase #5 $68.89   7.852%   $74.2992   $74.30   $74.30   $74.30  
  Purchase #6 $162.56   8.524%   $176.4166   $176.42   $176.40   $176.40  
  Purchase #7 $136.29   11.103%   $151.4223   $151.42   $151.40   $151.40  
  7 purchase totals = $933.26       $1,015.5794   $1,015.58   $1,015.55   $1,015.50