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 $195.81   8.603%   $212.6555   $212.66   $212.65   $212.70  
  Purchase #2 $230.95   8.836%   $251.3567   $251.36   $251.35   $251.40  
  Purchase #3 $39.30   13.409%   $44.5697   $44.57   $44.55   $44.60  
  Purchase #4 $106.33   13.526%   $120.7122   $120.71   $120.70   $120.70  
  Purchase #5 $127.76   12.438%   $143.6508   $143.65   $143.65   $143.70  
  Purchase #6 $70.72   4.601%   $73.9738   $73.97   $73.95   $74.00  
  Purchase #7 $178.34   6.138%   $189.2865   $189.29   $189.30   $189.30  
  7 purchase totals = $949.21       $1,036.2052   $1,036.21   $1,036.15   $1,036.40