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 $159.82   10.334%   $176.3358   $176.34   $176.35   $176.30  
  Purchase #2 $246.83   4.565%   $258.0978   $258.10   $258.10   $258.10  
  Purchase #3 $154.79   12.794%   $174.5938   $174.59   $174.60   $174.60  
  Purchase #4 $67.44   3.240%   $69.6251   $69.63   $69.65   $69.60  
  Purchase #5 $26.27   11.157%   $29.2009   $29.20   $29.20   $29.20  
  Purchase #6 $205.97   5.818%   $217.9533   $217.95   $217.95   $218.00  
  Purchase #7 $100.85   4.544%   $105.4326   $105.43   $105.45   $105.40  
  7 purchase totals = $961.97       $1,031.2393   $1,031.24   $1,031.30   $1,031.20