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 $191.56   6.382%   $203.7854   $203.79   $203.80   $203.80  
  Purchase #2 $45.29   9.470%   $49.579   $49.58   $49.60   $49.60  
  Purchase #3 $174.31   9.535%   $190.9305   $190.93   $190.95   $190.90  
  Purchase #4 $64.38   10.797%   $71.3311   $71.33   $71.35   $71.30  
  Purchase #5 $181.32   7.358%   $194.6615   $194.66   $194.65   $194.70  
  Purchase #6 $71.26   3.793%   $73.9629   $73.96   $73.95   $74.00  
  Purchase #7 $118.63   13.285%   $134.39   $134.39   $134.40   $134.40  
  7 purchase totals = $846.75       $918.6404   $918.64   $918.70   $918.70