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 $164.80   10.279%   $181.7398   $181.74   $181.75   $181.70  
  Purchase #2 $76.41   6.654%   $81.4943   $81.49   $81.50   $81.50  
  Purchase #3 $234.77   9.514%   $257.106   $257.11   $257.10   $257.10  
  Purchase #4 $201.55   5.172%   $211.9742   $211.97   $211.95   $212.00  
  Purchase #5 $57.41   8.678%   $62.392   $62.39   $62.40   $62.40  
  Purchase #6 $248.39   6.395%   $264.2745   $264.27   $264.25   $264.30  
  Purchase #7 $222.80   6.482%   $237.2419   $237.24   $237.25   $237.20  
  7 purchase totals = $1,206.13       $1,296.2227   $1,296.21   $1,296.20   $1,296.20