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 $175.35   8.808%   $190.7948   $190.79   $190.80   $190.80  
  Purchase #2 $70.59   6.133%   $74.9193   $74.92   $74.90   $74.90  
  Purchase #3 $248.40   6.409%   $264.32   $264.32   $264.30   $264.30  
  Purchase #4 $13.34   4.408%   $13.928   $13.93   $13.95   $13.90  
  Purchase #5 $200.57   9.315%   $219.2531   $219.25   $219.25   $219.30  
  Purchase #6 $38.96   5.293%   $41.0222   $41.02   $41.00   $41.00  
  Purchase #7 $250.83   5.648%   $264.9969   $265.00   $265.00   $265.00  
  7 purchase totals = $998.04       $1,069.2343   $1,069.23   $1,069.20   $1,069.20