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 $53.50   11.634%   $59.7242   $59.72   $59.70   $59.70  
  Purchase #2 $94.43   7.119%   $101.1525   $101.15   $101.15   $101.20  
  Purchase #3 $219.31   5.831%   $232.098   $232.10   $232.10   $232.10  
  Purchase #4 $45.99   8.782%   $50.0288   $50.03   $50.05   $50.00  
  Purchase #5 $94.68   12.339%   $106.3626   $106.36   $106.35   $106.40  
  Purchase #6 $163.43   7.857%   $176.2707   $176.27   $176.25   $176.30  
  Purchase #7 $232.68   5.711%   $245.9684   $245.97   $245.95   $246.00  
  7 purchase totals = $904.02       $971.6052   $971.60   $971.55   $971.70