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 $23.81   8.218%   $25.7667   $25.77   $25.75   $25.80  
  Purchase #2 $143.58   6.286%   $152.6054   $152.61   $152.60   $152.60  
  Purchase #3 $205.32   12.259%   $230.4902   $230.49   $230.50   $230.50  
  Purchase #4 $108.99   4.196%   $113.5632   $113.56   $113.55   $113.60  
  Purchase #5 $189.67   10.364%   $209.3274   $209.33   $209.35   $209.30  
  Purchase #6 $212.29   6.145%   $225.3352   $225.34   $225.35   $225.30  
  Purchase #7 $124.54   13.194%   $140.9718   $140.97   $140.95   $141.00  
  7 purchase totals = $1,008.20       $1,098.0599   $1,098.07   $1,098.05   $1,098.10