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 $92.37   3.737%   $95.8219   $95.82   $95.80   $95.80  
  Purchase #2 $207.46   13.293%   $235.0377   $235.04   $235.05   $235.00  
  Purchase #3 $22.65   8.343%   $24.5397   $24.54   $24.55   $24.50  
  Purchase #4 $212.68   11.764%   $237.6997   $237.70   $237.70   $237.70  
  Purchase #5 $100.40   5.218%   $105.6389   $105.64   $105.65   $105.60  
  Purchase #6 $39.28   4.763%   $41.1509   $41.15   $41.15   $41.20  
  Purchase #7 $145.85   12.739%   $164.4298   $164.43   $164.45   $164.40  
  7 purchase totals = $820.69       $904.3186   $904.32   $904.35   $904.20