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 $63.76   8.109%   $68.9303   $68.93   $68.95   $68.90  
  Purchase #2 $111.98   12.227%   $125.6718   $125.67   $125.65   $125.70  
  Purchase #3 $128.87   12.831%   $145.4053   $145.41   $145.40   $145.40  
  Purchase #4 $38.49   8.196%   $41.6446   $41.64   $41.65   $41.60  
  Purchase #5 $127.29   3.550%   $131.8088   $131.81   $131.80   $131.80  
  Purchase #6 $92.46   7.359%   $99.2641   $99.26   $99.25   $99.30  
  Purchase #7 $173.90   5.298%   $183.1132   $183.11   $183.10   $183.10  
  7 purchase totals = $736.75       $795.8381   $795.83   $795.80   $795.80