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 $92.41   3.649%   $95.782   $95.78   $95.80   $95.80  
  Purchase #2 $111.32   8.766%   $121.0783   $121.08   $121.10   $121.10  
  Purchase #3 $114.97   10.530%   $127.0763   $127.08   $127.10   $127.10  
  Purchase #4 $107.72   11.349%   $119.9451   $119.95   $119.95   $119.90  
  Purchase #5 $120.85   13.253%   $136.8663   $136.87   $136.85   $136.90  
  Purchase #6 $227.97   12.437%   $256.3226   $256.32   $256.30   $256.30  
  Purchase #7 $10.91   10.149%   $12.0173   $12.02   $12.00   $12.00  
  7 purchase totals = $786.15       $869.0879   $869.10   $869.10   $869.10