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 $63.31   8.294%   $68.5609   $68.56   $68.55   $68.60  
  Purchase #2 $229.40   5.336%   $241.6408   $241.64   $241.65   $241.60  
  Purchase #3 $191.32   13.658%   $217.4505   $217.45   $217.45   $217.50  
  Purchase #4 $249.54   13.758%   $283.8717   $283.87   $283.85   $283.90  
  Purchase #5 $59.83   12.864%   $67.5265   $67.53   $67.55   $67.50  
  Purchase #6 $58.51   10.339%   $64.5593   $64.56   $64.55   $64.60  
  Purchase #7 $10.69   12.686%   $12.0461   $12.05   $12.05   $12.00  
  7 purchase totals = $862.60       $955.6558   $955.66   $955.65   $955.70