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 $68.61   13.487%   $77.8634   $77.86   $77.85   $77.90  
  Purchase #2 $193.88   12.230%   $217.5915   $217.59   $217.60   $217.60  
  Purchase #3 $157.86   8.149%   $170.724   $170.72   $170.70   $170.70  
  Purchase #4 $149.79   5.245%   $157.6465   $157.65   $157.65   $157.60  
  Purchase #5 $7.48   12.504%   $8.4153   $8.42   $8.40   $8.40  
  Purchase #6 $147.39   12.154%   $165.3038   $165.30   $165.30   $165.30  
  Purchase #7 $244.85   3.575%   $253.6034   $253.60   $253.60   $253.60  
  7 purchase totals = $969.86       $1,051.1479   $1,051.14   $1,051.10   $1,051.10